diff --git a/3rd-party/class.jetpack-amp-support.php b/3rd-party/class.jetpack-amp-support.php
index 27f22d1bf78e..91d468acef4d 100644
--- a/3rd-party/class.jetpack-amp-support.php
+++ b/3rd-party/class.jetpack-amp-support.php
@@ -1,4 +1,7 @@
 <?php //phpcs:ignore WordPress.Files.FileName.InvalidClassFileName
+
+use Automattic\Jetpack\Sync\Functions;
+
 /**
  * Manages compatibility with the amp-wp plugin
  *
@@ -129,7 +132,7 @@ public static function amp_post_template_metadata( $metadata, $post ) {
 	 */
 	private static function add_site_icon_to_metadata( $metadata ) {
 		$size          = 60;
-		$site_icon_url = class_exists( 'Jetpack_Sync_Functions' ) ? Jetpack_Sync_Functions::site_icon_url( $size ) : '';
+		$site_icon_url = class_exists( 'Functions' ) ? Functions::site_icon_url( $size ) : '';
 
 		if ( function_exists( 'blavatar_domain' ) ) {
 			$metadata['publisher']['logo'] = array(
diff --git a/_inc/class.jetpack-provision.php b/_inc/class.jetpack-provision.php
index 819a77d588b0..7298f4fd3af1 100644
--- a/_inc/class.jetpack-provision.php
+++ b/_inc/class.jetpack-provision.php
@@ -1,5 +1,7 @@
 <?php //phpcs:ignore
 
+use Automattic\Jetpack\Sync\Actions;
+
 class Jetpack_Provision { //phpcs:ignore
 
 	/**
@@ -35,9 +37,9 @@ public static function register_and_build_request_body( $named_args ) {
 
 		// If Jetpack is currently connected, and is not in Safe Mode already, kick off a sync of the current
 		// functions/callables so that we can test if this site is in IDC.
-		if ( Jetpack::is_active() && ! Jetpack::validate_sync_error_idc_option() && Jetpack_Sync_Actions::sync_allowed() ) {
-			Jetpack_Sync_Actions::do_full_sync( array( 'functions' => true ) );
-			Jetpack_Sync_Actions::$sender->do_full_sync();
+		if ( Jetpack::is_active() && ! Jetpack::validate_sync_error_idc_option() && Actions::sync_allowed() ) {
+			Actions::do_full_sync( array( 'functions' => true ) );
+			Actions::$sender->do_full_sync();
 		}
 
 		if ( Jetpack::validate_sync_error_idc_option() ) {
diff --git a/_inc/lib/debugger/class-jetpack-debug-data.php b/_inc/lib/debugger/class-jetpack-debug-data.php
index 50642de30eb9..97a58767219c 100644
--- a/_inc/lib/debugger/class-jetpack-debug-data.php
+++ b/_inc/lib/debugger/class-jetpack-debug-data.php
@@ -5,6 +5,10 @@
  * @package jetpack
  */
 
+use Automattic\Jetpack\Sync\Functions;
+use Automattic\Jetpack\Sync\Modules;
+use Automattic\Jetpack\Sync\Sender;
+
 /**
  * Class Jetpack_Debug_Data
  *
@@ -266,14 +270,7 @@ public static function debug_data() {
 		);
 
 		/** Sync Debug Information */
-		/** Load Sync modules */
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-modules.php';
-		/** Load Sync sender */
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-sender.php';
-		/** Load Sync functions */
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-functions.php';
-
-		$sync_module = Jetpack_Sync_Modules::get_module( 'full-sync' );
+		$sync_module = Modules::get_module( 'full-sync' );
 		if ( $sync_module ) {
 			$sync_statuses              = $sync_module->get_status();
 			$human_readable_sync_status = array();
@@ -289,7 +286,7 @@ public static function debug_data() {
 			);
 		}
 
-		$queue = Jetpack_Sync_Sender::get_instance()->get_sync_queue();
+		$queue = Sender::get_instance()->get_sync_queue();
 
 		$debug_info['sync_size'] = array(
 			'label'   => 'Sync Queue Size',
@@ -302,7 +299,7 @@ public static function debug_data() {
 			'private' => false,
 		);
 
-		$full_sync_queue = Jetpack_Sync_Sender::get_instance()->get_full_sync_queue();
+		$full_sync_queue = Sender::get_instance()->get_full_sync_queue();
 
 		$debug_info['full_sync_size'] = array(
 			'label'   => 'Full Sync Queue Size',
@@ -321,8 +318,8 @@ public static function debug_data() {
 		 * Must follow sync debug since it depends on sync functionality.
 		 */
 		$idc_urls = array(
-			'home'       => Jetpack_Sync_Functions::home_url(),
-			'siteurl'    => Jetpack_Sync_Functions::site_url(),
+			'home'       => Functions::home_url(),
+			'siteurl'    => Functions::site_url(),
 			'WP_HOME'    => Jetpack_Constants::is_defined( 'WP_HOME' ) ? Jetpack_Constants::get_constant( 'WP_HOME' ) : '',
 			'WP_SITEURL' => Jetpack_Constants::is_defined( 'WP_SITEURL' ) ? Jetpack_Constants::get_constant( 'WP_SITEURL' ) : '',
 		);
diff --git a/class.jetpack-cli.php b/class.jetpack-cli.php
index 67ff87b59248..8a9c8b22f6eb 100644
--- a/class.jetpack-cli.php
+++ b/class.jetpack-cli.php
@@ -1,5 +1,10 @@
 <?php
 
+use Automattic\Jetpack\Sync\Actions;
+use Automattic\Jetpack\Sync\Listener;
+use Automattic\Jetpack\Sync\Queue;
+use Automattic\Jetpack\Sync\Settings;
+
 WP_CLI::add_command( 'jetpack', 'Jetpack_CLI' );
 
 /**
@@ -823,7 +828,7 @@ public function sync( $args, $assoc_args ) {
 
 		switch ( $action ) {
 			case 'status':
-				$status = Jetpack_Sync_Actions::get_sync_status();
+				$status = Actions::get_sync_status();
 				$collection = array();
 				foreach ( $status as $key => $item ) {
 					$collection[]  = array(
@@ -836,7 +841,7 @@ public function sync( $args, $assoc_args ) {
 				break;
 			case 'settings':
 				WP_CLI::log( __( 'Sync Settings:', 'jetpack' ) );
-				foreach( Jetpack_Sync_Settings::get_settings() as $setting => $item ) {
+				foreach( Settings::get_settings() as $setting => $item ) {
 					$settings[]  = array(
 						'setting' => $setting,
 						'value' => is_scalar( $item ) ? $item : json_encode( $item )
@@ -845,24 +850,23 @@ public function sync( $args, $assoc_args ) {
 				WP_CLI\Utils\format_items( 'table', $settings, array( 'setting', 'value' ) );
 
 			case 'disable':
-				// Don't set it via the Jetpack_Sync_Settings since that also resets the queues.
+				// Don't set it via the Settings since that also resets the queues.
 				update_option( 'jetpack_sync_settings_disable', 1 );
 				/* translators: %s is the site URL */
 				WP_CLI::log( sprintf( __( 'Sync Disabled on %s', 'jetpack' ), get_site_url() ) );
 				break;
 			case 'enable':
-				Jetpack_Sync_Settings::update_settings( array( 'disable' => 0 ) );
+				Settings::update_settings( array( 'disable' => 0 ) );
 				/* translators: %s is the site URL */
 				WP_CLI::log( sprintf( __( 'Sync Enabled on %s', 'jetpack' ), get_site_url() ) );
 				break;
 			case 'reset':
-				// Don't set it via the Jetpack_Sync_Settings since that also resets the queues.
+				// Don't set it via the Settings since that also resets the queues.
 				update_option( 'jetpack_sync_settings_disable', 1 );
 
 				/* translators: %s is the site URL */
 				WP_CLI::log( sprintf( __( 'Sync Disabled on %s. Use `wp jetpack sync enable` to enable syncing again.', 'jetpack' ), get_site_url() ) );
-				require_once dirname( __FILE__ ) . '/sync/class.jetpack-sync-listener.php';
-				$listener = Jetpack_Sync_Listener::get_instance();
+				$listener = Listener::get_instance();
 				if ( empty( $assoc_args['queue'] ) ) {
 					$listener->get_sync_queue()->reset();
 					$listener->get_full_sync_queue()->reset();
@@ -891,8 +895,8 @@ public function sync( $args, $assoc_args ) {
 
 				break;
 			case 'start':
-				if ( ! Jetpack_Sync_Actions::sync_allowed() ) {
-					if( ! Jetpack_Sync_Settings::get_setting( 'disable' ) ) {
+				if ( ! Actions::sync_allowed() ) {
+					if( ! Settings::get_setting( 'disable' ) ) {
 						WP_CLI::error( __( 'Jetpack sync is not currently allowed for this site. It is currently disabled. Run `wp jetpack sync enable` to enable it.', 'jetpack' ) );
 						return;
 					}
@@ -911,11 +915,11 @@ public function sync( $args, $assoc_args ) {
 
 				}
 				// Get the original settings so that we can restore them later
-				$original_settings = Jetpack_Sync_Settings::get_settings();
+				$original_settings = Settings::get_settings();
 
 				// Initialize sync settigns so we can sync as quickly as possible
 				$sync_settings = wp_parse_args(
-					array_intersect_key( $assoc_args, Jetpack_Sync_Settings::$valid_settings ),
+					array_intersect_key( $assoc_args, Settings::$valid_settings ),
 					array(
 						'sync_wait_time' => 0,
 						'enqueue_wait_time' => 0,
@@ -923,7 +927,7 @@ public function sync( $args, $assoc_args ) {
 						'max_queue_size_full_sync' => 100000
 					)
 				);
-				Jetpack_Sync_Settings::update_settings( $sync_settings );
+				Settings::update_settings( $sync_settings );
 
 				// Convert comma-delimited string of modules to an array
 				if ( ! empty( $assoc_args['modules'] ) ) {
@@ -954,7 +958,7 @@ public function sync( $args, $assoc_args ) {
 				}
 
 				// Kick off a full sync
-				if ( Jetpack_Sync_Actions::do_full_sync( $modules ) ) {
+				if ( Actions::do_full_sync( $modules ) ) {
 					if ( $modules ) {
 						/* translators: %s is a comma separated list of Jetpack modules */
 						WP_CLI::log( sprintf( __( 'Initialized a new full sync with modules: %s', 'jetpack' ), join( ', ', array_keys( $modules ) ) ) );
@@ -964,7 +968,7 @@ public function sync( $args, $assoc_args ) {
 				} else {
 
 					// Reset sync settings to original.
-					Jetpack_Sync_Settings::update_settings( $original_settings );
+					Settings::update_settings( $original_settings );
 
 					if ( $modules ) {
 						/* translators: %s is a comma separated list of Jetpack modules */
@@ -977,7 +981,7 @@ public function sync( $args, $assoc_args ) {
 				// Keep sending to WPCOM until there's nothing to send
 				$i = 1;
 				do {
-					$result = Jetpack_Sync_Actions::$sender->do_full_sync();
+					$result = Actions::$sender->do_full_sync();
 					if ( is_wp_error( $result ) ) {
 						$queue_empty_error = ( 'empty_queue_full_sync' == $result->get_error_code() );
 						if ( ! $queue_empty_error || ( $queue_empty_error && ( 1 == $i ) ) ) {
@@ -995,7 +999,7 @@ public function sync( $args, $assoc_args ) {
 				} while ( $result && ! is_wp_error( $result ) );
 
 				// Reset sync settings to original.
-				Jetpack_Sync_Settings::update_settings( $original_settings );
+				Settings::update_settings( $original_settings );
 
 				WP_CLI::success( __( 'Finished syncing to WordPress.com', 'jetpack' ) );
 				break;
@@ -1016,7 +1020,7 @@ public function sync( $args, $assoc_args ) {
 	 * @synopsis <incremental|full_sync> <peek>
 	 */
 	public function sync_queue( $args, $assoc_args ) {
-		if ( ! Jetpack_Sync_Actions::sync_allowed() ) {
+		if ( ! Actions::sync_allowed() ) {
 			WP_CLI::error( __( 'Jetpack sync is not currently allowed for this site.', 'jetpack' ) );
 		}
 
@@ -1033,8 +1037,7 @@ public function sync_queue( $args, $assoc_args ) {
 
 		switch( $action ) {
 			case 'peek':
-				require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-queue.php';
-				$queue = new Jetpack_Sync_Queue( $mapped_queue_name );
+				$queue = new Queue( $mapped_queue_name );
 				$items = $queue->peek( 100 );
 
 				if ( empty( $items ) ) {
diff --git a/class.jetpack-xmlrpc-server.php b/class.jetpack-xmlrpc-server.php
index 3ca6411d0176..7aaaa6046058 100644
--- a/class.jetpack-xmlrpc-server.php
+++ b/class.jetpack-xmlrpc-server.php
@@ -1,5 +1,9 @@
 <?php
 
+use Automattic\Jetpack\Sync\Functions;
+use Automattic\Jetpack\Sync\Modules;
+use Automattic\Jetpack\Sync\Sender;
+
 /**
  * Just a sack of functions.  Not actually an IXR_Server
  */
@@ -634,11 +638,9 @@ function unlink_user() {
 	function sync_object( $args ) {
 		// e.g. posts, post, 5
 		list( $module_name, $object_type, $id ) = $args;
-		require_once dirname( __FILE__ ) . '/sync/class.jetpack-sync-modules.php';
-		require_once dirname( __FILE__ ) . '/sync/class.jetpack-sync-sender.php';
 
-		$sync_module = Jetpack_Sync_Modules::get_module( $module_name );
-		$codec = Jetpack_Sync_Sender::get_instance()->get_codec();
+		$sync_module = Modules::get_module( $module_name );
+		$codec = Sender::get_instance()->get_codec();
 
 		return $codec->encode( $sync_module->get_object_by_id( $object_type, $id ) );
 	}
@@ -651,10 +653,9 @@ function sync_object( $args ) {
 	 * @return array
 	 */
 	function validate_urls_for_idc_mitigation() {
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-functions.php';
 		return array(
-			'home'    => Jetpack_Sync_Functions::home_url(),
-			'siteurl' => Jetpack_Sync_Functions::site_url(),
+			'home'    => Functions::home_url(),
+			'siteurl' => Functions::site_url(),
 		);
 	}
 
diff --git a/class.jetpack.php b/class.jetpack.php
index c572f1f4e73f..def18b5b679d 100644
--- a/class.jetpack.php
+++ b/class.jetpack.php
@@ -22,6 +22,10 @@
 	Flag for "activating" the plugin on sites where the activation hook never fired (auto-installs)
 */
 
+use Automattic\Jetpack\Sync\Functions;
+use Automattic\Jetpack\Sync\Sender;
+use Automattic\Jetpack\Sync\Users;
+
 require_once( JETPACK__PLUGIN_DIR . '_inc/lib/class.media.php' );
 
 class Jetpack {
@@ -1449,8 +1453,8 @@ public static function file_system_write_access() {
 	 * @return string ( '1' | '0' )
 	 **/
 	public static function is_version_controlled() {
-		_deprecated_function( __METHOD__, 'jetpack-4.2', 'Jetpack_Sync_Functions::is_version_controlled' );
-		return (string) (int) Jetpack_Sync_Functions::is_version_controlled();
+		_deprecated_function( __METHOD__, 'jetpack-4.2', 'Functions::is_version_controlled' );
+		return (string) (int) Functions::is_version_controlled();
 	}
 
 	/**
@@ -1804,8 +1808,8 @@ function extra_oembed_providers() {
 	 * Synchronize connected user role changes
 	 */
 	function user_role_change( $user_id ) {
-		_deprecated_function( __METHOD__, 'jetpack-4.2', 'Jetpack_Sync_Users::user_role_change()' );
-		Jetpack_Sync_Users::user_role_change( $user_id );
+		_deprecated_function( __METHOD__, 'jetpack-4.2', 'Users::user_role_change()' );
+		Users::user_role_change( $user_id );
 	}
 
 	/**
@@ -3357,8 +3361,7 @@ public static function disconnect( $update_activated_state = true ) {
 		delete_transient( $transient_key );
 
 		// Delete all the sync related data. Since it could be taking up space.
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-sender.php';
-		Jetpack_Sync_Sender::get_instance()->uninstall();
+		Sender::get_instance()->uninstall();
 
 		// Disable the Heartbeat cron
 		Jetpack_Heartbeat::init()->deactivate();
@@ -6209,10 +6212,9 @@ public static function get_sync_error_idc_option( $response = array() ) {
 		// in a transient to allow for autoloading and caching on subsequent views.
 		$local_options = get_transient( 'jetpack_idc_local' );
 		if ( false === $local_options ) {
-			require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-functions.php';
 			$local_options = array(
-				'home'    => Jetpack_Sync_Functions::home_url(),
-				'siteurl' => Jetpack_Sync_Functions::site_url(),
+				'home'    => Functions::home_url(),
+				'siteurl' => Functions::site_url(),
 			);
 			set_transient( 'jetpack_idc_local', $local_options, MINUTE_IN_SECONDS );
 		}
diff --git a/composer.json b/composer.json
index d62789bde481..6759f8079da3 100644
--- a/composer.json
+++ b/composer.json
@@ -9,7 +9,8 @@
 	},
 	"require": {
 		"ext-openssl": "*",
-		"automattic/jetpack-logo": "@dev"
+		"automattic/jetpack-logo": "@dev",
+		"automattic/jetpack-sync": "@dev"
 	},
 	"require-dev": {
 		"dealerdirect/phpcodesniffer-composer-installer": "0.5.0",
diff --git a/composer.lock b/composer.lock
index 48df1ee81d8c..520e0e62c96f 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "167f5c90d0f8c7224fdc8707e1ba107f",
+    "content-hash": "3441d93f564ebc5e82e349fe9db3a39c",
     "packages": [
         {
             "name": "automattic/jetpack-logo",
@@ -25,6 +25,26 @@
                 "GPL-2.0-or-later"
             ],
             "description": "A logo for Jetpack"
+        },
+        {
+            "name": "automattic/jetpack-sync",
+            "version": "dev-try/sync-package",
+            "dist": {
+                "type": "path",
+                "url": "./packages/sync",
+                "reference": "bf7f14e0d3d9618cfad03c0a90fa5b0dd7528fbc",
+                "shasum": null
+            },
+            "type": "library",
+            "autoload": {
+                "psr-4": {
+                    "Automattic\\Jetpack\\Sync\\": "src/"
+                }
+            },
+            "license": [
+                "GPL-2.0-or-later"
+            ],
+            "description": "A library that allows syncing to the WP.com infrastructure."
         }
     ],
     "packages-dev": [
@@ -399,7 +419,8 @@
     "aliases": [],
     "minimum-stability": "stable",
     "stability-flags": {
-        "automattic/jetpack-logo": 20
+        "automattic/jetpack-logo": 20,
+        "automattic/jetpack-sync": 20
     },
     "prefer-stable": false,
     "prefer-lowest": false,
diff --git a/jetpack.php b/jetpack.php
index cf934b3670d6..4435d708e0c6 100644
--- a/jetpack.php
+++ b/jetpack.php
@@ -208,7 +208,6 @@ function jetpack_admin_missing_autoloader() { ?>
 require_once( JETPACK__PLUGIN_DIR . 'class.jetpack-client.php'        );
 require_once( JETPACK__PLUGIN_DIR . 'class.jetpack-data.php'          );
 require_once( JETPACK__PLUGIN_DIR . 'class.jetpack-client-server.php' );
-require_once( JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-actions.php' );
 require_once( JETPACK__PLUGIN_DIR . 'class.jetpack-options.php'       );
 require_once( JETPACK__PLUGIN_DIR . 'class.jetpack-user-agent.php'    );
 require_once( JETPACK__PLUGIN_DIR . 'class.jetpack-post-images.php'   );
diff --git a/json-endpoints/jetpack/class.jetpack-json-api-plugins-endpoint.php b/json-endpoints/jetpack/class.jetpack-json-api-plugins-endpoint.php
index 1df4fe667121..d4877f8be7a6 100644
--- a/json-endpoints/jetpack/class.jetpack-json-api-plugins-endpoint.php
+++ b/json-endpoints/jetpack/class.jetpack-json-api-plugins-endpoint.php
@@ -1,5 +1,7 @@
 <?php
 
+use Automattic\Jetpack\Sync\Functions;
+
 /**
  * Base class for working with plugins.
  */
@@ -200,7 +202,7 @@ protected function get_file_mod_capabilities() {
 		$reasons_can_not_autoupdate = array();
 		$reasons_can_not_modify_files = array();
 
-		$has_file_system_write_access = Jetpack_Sync_Functions::file_system_write_access();
+		$has_file_system_write_access = Functions::file_system_write_access();
 		if ( ! $has_file_system_write_access ) {
 			$reasons_can_not_modify_files['has_no_file_system_write_access'] =  __( 'The file permissions on this host prevent editing files.', 'jetpack' );
 		}
@@ -315,7 +317,6 @@ protected function get_plugin_updates( $plugin_file ) {
 	}
 
 	protected function get_plugin_action_links( $plugin_file ) {
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-functions.php';
-		return Jetpack_Sync_Functions::get_plugins_action_links( $plugin_file );
+		return Functions::get_plugins_action_links( $plugin_file );
 	}
 }
diff --git a/json-endpoints/jetpack/class.jetpack-json-api-sync-endpoint.php b/json-endpoints/jetpack/class.jetpack-json-api-sync-endpoint.php
index 9bd14bb104fc..e288a46f7526 100644
--- a/json-endpoints/jetpack/class.jetpack-json-api-sync-endpoint.php
+++ b/json-endpoints/jetpack/class.jetpack-json-api-sync-endpoint.php
@@ -1,5 +1,13 @@
 <?php
 
+use Automattic\Jetpack\Sync\Actions;
+use Automattic\Jetpack\Sync\Modules;
+use Automattic\Jetpack\Sync\Queue;
+use Automattic\Jetpack\Sync\Queue_Buffer;
+use Automattic\Jetpack\Sync\Sender;
+use Automattic\Jetpack\Sync\Settings;
+use Automattic\Jetpack\Sync\WP_Replicastore;
+
 // POST /sites/%s/sync
 class Jetpack_JSON_API_Sync_Endpoint extends Jetpack_JSON_API_Endpoint {
 	protected $needed_capabilities = 'manage_options';
@@ -32,7 +40,7 @@ protected function result() {
 		if ( empty( $modules ) ) {
 			$modules = null;
 		}
-		return array( 'scheduled' => Jetpack_Sync_Actions::do_full_sync( $modules ) );
+		return array( 'scheduled' => Actions::do_full_sync( $modules ) );
 	}
 
 	protected function validate_queue( $query ) {
@@ -52,15 +60,14 @@ class Jetpack_JSON_API_Sync_Status_Endpoint extends Jetpack_JSON_API_Sync_Endpoi
 	protected function result() {
 		$args   = $this->query_args();
 		$fields = isset( $args['fields'] ) ? $args['fields'] : array();
-		return Jetpack_Sync_Actions::get_sync_status( $fields );
+		return Actions::get_sync_status( $fields );
 	}
 }
 
 // GET /sites/%s/data-check
 class Jetpack_JSON_API_Sync_Check_Endpoint extends Jetpack_JSON_API_Sync_Endpoint {
 	protected function result() {
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-wp-replicastore.php';
-		$store = new Jetpack_Sync_WP_Replicastore();
+		$store = new WP_Replicastore();
 		return $store->checksum_all();
 	}
 }
@@ -76,8 +83,7 @@ protected function result() {
 			$columns = null; // go with defaults
 		}
 
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-wp-replicastore.php';
-		$store = new Jetpack_Sync_WP_Replicastore();
+		$store = new WP_Replicastore();
 
 		if ( ! isset( $args['strip_non_ascii'] ) ) {
 			$args['strip_non_ascii'] = true;
@@ -93,9 +99,7 @@ class Jetpack_JSON_API_Sync_Modify_Settings_Endpoint extends Jetpack_JSON_API_Sy
 	protected function result() {
 		$args = $this->input();
 
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-settings.php';
-
-		$sync_settings = Jetpack_Sync_Settings::get_settings();
+		$sync_settings = Settings::get_settings();
 
 		foreach ( $args as $key => $value ) {
 			if ( $value !== false ) {
@@ -112,19 +116,17 @@ protected function result() {
 			}
 		}
 
-		Jetpack_Sync_Settings::update_settings( $sync_settings );
+		Settings::update_settings( $sync_settings );
 
 		// re-fetch so we see what's really being stored
-		return Jetpack_Sync_Settings::get_settings();
+		return Settings::get_settings();
 	}
 }
 
 // GET /sites/%s/sync/settings
 class Jetpack_JSON_API_Sync_Get_Settings_Endpoint extends Jetpack_JSON_API_Sync_Endpoint {
 	protected function result() {
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-settings.php';
-
-		return Jetpack_Sync_Settings::get_settings();
+		return Settings::get_settings();
 	}
 }
 
@@ -135,21 +137,18 @@ protected function result() {
 
 		$module_name = $args['module_name'];
 
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-modules.php';
-
-		if ( ! $sync_module = Jetpack_Sync_Modules::get_module( $module_name ) ) {
+		if ( ! $sync_module = Modules::get_module( $module_name ) ) {
 			return new WP_Error( 'invalid_module', 'You specified an invalid sync module' );
 		}
 
 		$object_type = $args['object_type'];
 		$object_ids  = $args['object_ids'];
 
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-sender.php';
-		$codec = Jetpack_Sync_Sender::get_instance()->get_codec();
+		$codec = Sender::get_instance()->get_codec();
 
-		Jetpack_Sync_Settings::set_is_syncing( true );
+		Settings::set_is_syncing( true );
 		$objects = $codec->encode( $sync_module->get_objects_by_id( $object_type, $object_ids ) );
-		Jetpack_Sync_Settings::set_is_syncing( false );
+		Settings::set_is_syncing( false );
 
 		return array(
 			'objects' => $objects,
@@ -167,10 +166,8 @@ protected function result() {
 			return $queue_name;
 		}
 
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-sender.php';
-
-		$sender = Jetpack_Sync_Sender::get_instance();
-		$response = $sender->do_sync_for_queue( new Jetpack_Sync_Queue( $args['queue'] ) );
+		$sender = Sender::get_instance();
+		$response = $sender->do_sync_for_queue( new Queue( $args['queue'] ) );
 
 		return array(
 			'response' => $response
@@ -191,15 +188,13 @@ protected function result() {
 			return new WP_Error( 'invalid_number_of_items', 'Number of items needs to be an integer that is larger than 0 and less then 100', 400 );
 		}
 
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-queue.php';
-		$queue = new Jetpack_Sync_Queue( $queue_name );
+		$queue = new Queue( $queue_name );
 
 		if ( 0 === $queue->size() ) {
 			return new WP_Error( 'queue_size', 'The queue is empty and there is nothing to send', 400 );
 		}
 
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-sender.php';
-		$sender = Jetpack_Sync_Sender::get_instance();
+		$sender = Sender::get_instance();
 
 		// try to give ourselves as much time as possible
 		set_time_limit( 0 );
@@ -220,9 +215,9 @@ protected function result() {
 			return new WP_Error( 'buffer_non-object', 'Buffer is not an object', 400 );
 		}
 
-		Jetpack_Sync_Settings::set_is_syncing( true );
+		Settings::set_is_syncing( true );
 		list( $items_to_send, $skipped_items_ids, $items ) = $sender->get_items_to_send( $buffer, $args['encode'] );
-		Jetpack_Sync_Settings::set_is_syncing( false );
+		Settings::set_is_syncing( false );
 
 		return array(
 			'buffer_id'      => $buffer->id,
@@ -262,7 +257,6 @@ protected function result() {
 		if ( is_wp_error( $queue_name ) ) {
 			return $queue_name;
 		}
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-queue.php';
 
 		if ( ! isset( $request_body['buffer_id'] ) ) {
 			return new WP_Error( 'missing_buffer_id', 'Please provide a buffer id', 400 );
@@ -276,8 +270,8 @@ protected function result() {
 		$request_body ['buffer_id'] = preg_replace( '/[^A-Za-z0-9]/', '', $request_body['buffer_id'] );
 		$request_body['item_ids'] = array_filter( array_map( array( 'Jetpack_JSON_API_Sync_Close_Endpoint', 'sanitize_item_ids' ), $request_body['item_ids'] ) );
 
-		$buffer = new Jetpack_Sync_Queue_Buffer( $request_body['buffer_id'], $request_body['item_ids'] );
-		$queue = new Jetpack_Sync_Queue( $queue_name );
+		$buffer = new Queue_Buffer( $request_body['buffer_id'], $request_body['item_ids'] );
+		$queue = new Queue( $queue_name );
 
 		$response = $queue->close( $buffer, $request_body['item_ids'] );
 
@@ -312,8 +306,7 @@ protected function result() {
 			return new WP_Error( 'invalid_queue', 'Queue name should be sync or full_sync', 400 );
 		}
 
-		require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-queue.php';
-		$queue = new Jetpack_Sync_Queue( $args['queue'] );
+		$queue = new Queue( $args['queue'] );
 
 		// False means that there was no lock to delete.
 		$response = $queue->unlock();
diff --git a/json-endpoints/jetpack/class.wpcom-json-api-get-option-endpoint.php b/json-endpoints/jetpack/class.wpcom-json-api-get-option-endpoint.php
index 3a76256f6249..b261f202c5f6 100644
--- a/json-endpoints/jetpack/class.wpcom-json-api-get-option-endpoint.php
+++ b/json-endpoints/jetpack/class.wpcom-json-api-get-option-endpoint.php
@@ -1,5 +1,7 @@
 <?php
 
+use Automattic\Jetpack\Sync\Defaults;
+
 class WPCOM_JSON_API_Get_Option_Endpoint extends Jetpack_JSON_API_Endpoint {
 
 	protected $needed_capabilities = 'manage_options';
@@ -22,7 +24,6 @@ function validate_input( $object ) {
 		}
 		$this->site_option = isset( $query_args['site_option'] ) ? $query_args['site_option'] : false;
 
-		require_once JETPACK__PLUGIN_DIR . '/sync/class.jetpack-sync-defaults.php';
 		/**
 		 * Filter the list of options that are manageable via the JSON API.
 		 *
@@ -33,7 +34,7 @@ function validate_input( $object ) {
 		 * @param array The default list of site options.
 		 * @param bool Is the option a site option.
 		 */
-		if ( ! in_array( $this->option_name, apply_filters( 'jetpack_options_whitelist', Jetpack_Sync_Defaults::$default_options_whitelist, $this->site_option ) ) ) {
+		if ( ! in_array( $this->option_name, apply_filters( 'jetpack_options_whitelist', Defaults::$default_options_whitelist, $this->site_option ) ) ) {
 			return new WP_Error( 'option_name_not_in_whitelist', __( 'You must specify a whitelisted option_name', 'jetpack' ) );
 		}
 		return true;
diff --git a/modules/contact-form/grunion-contact-form.php b/modules/contact-form/grunion-contact-form.php
index a26dc20c1d7e..3c64a88c0643 100644
--- a/modules/contact-form/grunion-contact-form.php
+++ b/modules/contact-form/grunion-contact-form.php
@@ -10,6 +10,8 @@
 License: GPLv2 or later
 */
 
+use Automattic\Jetpack\Sync\Settings;
+
 define( 'GRUNION_PLUGIN_DIR', plugin_dir_path( __FILE__ ) );
 define( 'GRUNION_PLUGIN_URL', plugin_dir_url( __FILE__ ) );
 
@@ -1935,8 +1937,7 @@ static function _style_on() {
 	 * @return string HTML for the concat form.
 	 */
 	static function parse( $attributes, $content ) {
-		require_once JETPACK__PLUGIN_DIR . '/sync/class.jetpack-sync-settings.php';
-		if ( Jetpack_Sync_Settings::is_syncing() ) {
+		if ( Settings::is_syncing() ) {
 			return '';
 		}
 		// Create a new Grunion_Contact_Form object (this class)
diff --git a/modules/likes/jetpack-likes-settings.php b/modules/likes/jetpack-likes-settings.php
index 390fea1e039a..a172603bd761 100644
--- a/modules/likes/jetpack-likes-settings.php
+++ b/modules/likes/jetpack-likes-settings.php
@@ -1,5 +1,7 @@
 <?php
 
+use Automattic\Jetpack\Sync\Settings;
+
 class Jetpack_Likes_Settings {
 	function __construct() {
 		$this->in_jetpack = ! ( defined( 'IS_WPCOM' ) && IS_WPCOM );
@@ -269,8 +271,7 @@ function is_post_likeable( $post_id = 0 ) {
 	 * similar logic and filters apply here, too.
 	 */
 	function is_likes_visible() {
-		require_once JETPACK__PLUGIN_DIR . '/sync/class.jetpack-sync-settings.php';
-		if ( Jetpack_Sync_Settings::is_syncing() ) {
+		if ( Settings::is_syncing() ) {
 			return false;
 		}
 
diff --git a/modules/related-posts/jetpack-related-posts.php b/modules/related-posts/jetpack-related-posts.php
index f1d1007b79ac..7889e3f97fc5 100644
--- a/modules/related-posts/jetpack-related-posts.php
+++ b/modules/related-posts/jetpack-related-posts.php
@@ -1,4 +1,7 @@
 <?php
+
+use Automattic\Jetpack\Sync\Settings;
+
 class Jetpack_RelatedPosts {
 	const VERSION   = '20190204';
 	const SHORTCODE = 'jetpack-related-posts';
@@ -197,8 +200,7 @@ public function test_for_shortcode( $content ) {
 	 * @returns string
 	 */
 	public function get_target_html() {
-		require_once JETPACK__PLUGIN_DIR . '/sync/class.jetpack-sync-settings.php';
-		if ( Jetpack_Sync_Settings::is_syncing() ) {
+		if ( Settings::is_syncing() ) {
 			return '';
 		}
 
@@ -232,8 +234,7 @@ public function get_target_html() {
 	 * @returns string
 	 */
 	public function get_target_html_unsupported() {
-		require_once JETPACK__PLUGIN_DIR . '/sync/class.jetpack-sync-settings.php';
-		if ( Jetpack_Sync_Settings::is_syncing() ) {
+		if ( Settings::is_syncing() ) {
 			return '';
 		}
 		return "\n\n<!-- Jetpack Related Posts is not supported in this context. -->\n\n";
diff --git a/modules/sharedaddy/sharing-service.php b/modules/sharedaddy/sharing-service.php
index 382b1f3b8b1c..748511859383 100644
--- a/modules/sharedaddy/sharing-service.php
+++ b/modules/sharedaddy/sharing-service.php
@@ -1,5 +1,7 @@
 <?php
 
+use Automattic\Jetpack\Sync\Settings;
+
 include_once dirname( __FILE__ ) . '/sharing-sources.php';
 
 define( 'WP_SHARING_PLUGIN_VERSION', JETPACK__VERSION );
@@ -669,8 +671,7 @@ function sharing_process_requests() {
 function sharing_display( $text = '', $echo = false ) {
 	global $post, $wp_current_filter;
 
-	require_once JETPACK__PLUGIN_DIR . '/sync/class.jetpack-sync-settings.php';
-	if ( Jetpack_Sync_Settings::is_syncing() ) {
+	if ( Settings::is_syncing() ) {
 		return $text;
 	}
 
diff --git a/packages/sync/composer.json b/packages/sync/composer.json
new file mode 100644
index 000000000000..eaf18fc53e49
--- /dev/null
+++ b/packages/sync/composer.json
@@ -0,0 +1,12 @@
+{
+	"name": "automattic/jetpack-sync",
+	"description": "A library that allows syncing to the WP.com infrastructure.",
+	"type": "library",
+	"license": "GPL-2.0-or-later",
+	"require": {},
+	"autoload": {
+		"psr-4": {
+			"Automattic\\Jetpack\\Sync\\": "src/"
+		}
+	}
+}
diff --git a/sync/class.jetpack-sync-actions.php b/packages/sync/src/Actions.php
similarity index 79%
rename from sync/class.jetpack-sync-actions.php
rename to packages/sync/src/Actions.php
index 3f137d840e8d..82c95c715509 100644
--- a/sync/class.jetpack-sync-actions.php
+++ b/packages/sync/src/Actions.php
@@ -1,6 +1,6 @@
 <?php
 
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-modules.php';
+namespace Automattic\Jetpack\Sync;
 
 /**
  * The role of this class is to hook the Sync subsystem into WordPress - when to listen for actions,
@@ -8,7 +8,7 @@
  *
  * It also binds the action to send data to WPCOM to Jetpack's XMLRPC client object.
  */
-class Jetpack_Sync_Actions {
+class Actions {
 	static $sender                         = null;
 	static $listener                       = null;
 	const DEFAULT_SYNC_CRON_INTERVAL_NAME  = 'jetpack_sync_interval';
@@ -29,9 +29,6 @@ static function init() {
 		// When importing via cron, do not sync
 		add_action( 'wp_cron_importer_hook', array( __CLASS__, 'set_is_importing_true' ), 1 );
 
-		// Sync connected user role changes to .com
-		require_once dirname( __FILE__ ) . '/class.jetpack-sync-users.php';
-
 		// publicize filter to prevent publicizing blacklisted post types
 		add_filter( 'publicize_should_publicize_published_post', array( __CLASS__, 'prevent_publicize_blacklisted_posts' ), 10, 2 );
 
@@ -78,7 +75,7 @@ static function add_sender_shutdown() {
 	}
 
 	static function should_initialize_sender() {
-		if ( Jetpack_Constants::is_true( 'DOING_CRON' ) ) {
+		if ( \Jetpack_Constants::is_true( 'DOING_CRON' ) ) {
 			return self::sync_via_cron_allowed();
 		}
 
@@ -105,17 +102,17 @@ static function sync_allowed() {
 		if ( defined( 'PHPUNIT_JETPACK_TESTSUITE' ) ) {
 			return true;
 		}
-		require_once dirname( __FILE__ ) . '/class.jetpack-sync-settings.php';
-		if ( ! Jetpack_Sync_Settings::is_sync_enabled() ) {
+
+		if ( ! Settings::is_sync_enabled() ) {
 			return false;
 		}
-		if ( Jetpack::is_development_mode() ) {
+		if ( \Jetpack::is_development_mode() ) {
 			return false;
 		}
-		if ( Jetpack::is_staging_site() ) {
+		if ( \Jetpack::is_staging_site() ) {
 			return false;
 		}
-		if ( ! Jetpack::is_active() ) {
+		if ( ! \Jetpack::is_active() ) {
 			if ( ! doing_action( 'jetpack_user_authorized' ) ) {
 				return false;
 			}
@@ -125,13 +122,11 @@ static function sync_allowed() {
 	}
 
 	static function sync_via_cron_allowed() {
-		require_once dirname( __FILE__ ) . '/class.jetpack-sync-settings.php';
-		return ( Jetpack_Sync_Settings::get_setting( 'sync_via_cron' ) );
+		return ( Settings::get_setting( 'sync_via_cron' ) );
 	}
 
 	static function prevent_publicize_blacklisted_posts( $should_publicize, $post ) {
-		require_once dirname( __FILE__ ) . '/class.jetpack-sync-settings.php';
-		if ( in_array( $post->post_type, Jetpack_Sync_Settings::get_setting( 'post_types_blacklist' ) ) ) {
+		if ( in_array( $post->post_type, Settings::get_setting( 'post_types_blacklist' ) ) ) {
 			return false;
 		}
 
@@ -139,35 +134,33 @@ static function prevent_publicize_blacklisted_posts( $should_publicize, $post )
 	}
 
 	static function set_is_importing_true() {
-		require_once dirname( __FILE__ ) . '/class.jetpack-sync-settings.php';
-		Jetpack_Sync_Settings::set_importing( true );
+		Settings::set_importing( true );
 	}
 
 	static function send_data( $data, $codec_name, $sent_timestamp, $queue_id, $checkout_duration, $preprocess_duration ) {
-		require_once dirname( __FILE__ ) . '/class.jetpack-sync-functions.php';
-		Jetpack::load_xml_rpc_client();
+		\Jetpack::load_xml_rpc_client();
 
 		$query_args = array(
 			'sync'      => '1',             // add an extra parameter to the URL so we can tell it's a sync action
 			'codec'     => $codec_name,     // send the name of the codec used to encode the data
 			'timestamp' => $sent_timestamp, // send current server time so we can compensate for clock differences
 			'queue'     => $queue_id,       // sync or full_sync
-			'home'      => Jetpack_Sync_Functions::home_url(),  // Send home url option to check for Identity Crisis server-side
-			'siteurl'   => Jetpack_Sync_Functions::site_url(),  // Send siteurl option to check for Identity Crisis server-side
+			'home'      => Functions::home_url(),  // Send home url option to check for Identity Crisis server-side
+			'siteurl'   => Functions::site_url(),  // Send siteurl option to check for Identity Crisis server-side
 			'cd'        => sprintf( '%.4f', $checkout_duration ),   // Time spent retrieving queue items from the DB
 			'pd'        => sprintf( '%.4f', $preprocess_duration ), // Time spent converting queue items into data to send
 		);
 
 		// Has the site opted in to IDC mitigation?
-		if ( Jetpack::sync_idc_optin() ) {
+		if ( \Jetpack::sync_idc_optin() ) {
 			$query_args['idc'] = true;
 		}
 
-		if ( Jetpack_Options::get_option( 'migrate_for_idc', false ) ) {
+		if ( \Jetpack_Options::get_option( 'migrate_for_idc', false ) ) {
 			$query_args['migrate_for_idc'] = true;
 		}
 
-		$query_args['timeout'] = Jetpack_Sync_Settings::is_doing_cron() ? 30 : 15;
+		$query_args['timeout'] = Settings::is_doing_cron() ? 30 : 15;
 
 		/**
 		 * Filters query parameters appended to the Sync request URL sent to WordPress.com.
@@ -178,9 +171,9 @@ static function send_data( $data, $codec_name, $sent_timestamp, $queue_id, $chec
 		 */
 		$query_args = apply_filters( 'jetpack_sync_send_data_query_args', $query_args );
 
-		$url = add_query_arg( $query_args, Jetpack::xmlrpc_api_url() );
+		$url = add_query_arg( $query_args, \Jetpack::xmlrpc_api_url() );
 
-		$rpc = new Jetpack_IXR_Client(
+		$rpc = new \Jetpack_IXR_Client(
 			array(
 				'url'     => $url,
 				'user_id' => JETPACK_MASTER_USER,
@@ -206,13 +199,13 @@ static function send_data( $data, $codec_name, $sent_timestamp, $queue_id, $chec
 			);
 
 			if ( in_array( $error_code, $allowed_idc_error_codes ) ) {
-				Jetpack_Options::update_option(
+				\Jetpack_Options::update_option(
 					'sync_error_idc',
-					Jetpack::get_sync_error_idc_option( $response )
+					\Jetpack::get_sync_error_idc_option( $response )
 				);
 			}
 
-			return new WP_Error(
+			return new \WP_Error(
 				'sync_error_idc',
 				esc_html__( 'Sync has been blocked from WordPress.com because it would cause an identity crisis', 'jetpack' )
 			);
@@ -246,7 +239,7 @@ static function do_full_sync( $modules = null ) {
 			return false;
 		}
 
-		$full_sync_module = Jetpack_Sync_Modules::get_module( 'full-sync' );
+		$full_sync_module = Modules::get_module( 'full-sync' );
 
 		if ( ! $full_sync_module ) {
 			return false;
@@ -294,7 +287,7 @@ static function do_cron_sync_by_type( $type ) {
 
 		self::initialize_sender();
 
-		$time_limit = Jetpack_Sync_Settings::get_setting( 'cron_sync_time_limit' );
+		$time_limit = Settings::get_setting( 'cron_sync_time_limit' );
 		$start_time = time();
 
 		do {
@@ -314,28 +307,25 @@ static function do_cron_sync_by_type( $type ) {
 	}
 
 	static function initialize_listener() {
-		require_once dirname( __FILE__ ) . '/class.jetpack-sync-listener.php';
-		self::$listener = Jetpack_Sync_Listener::get_instance();
+		self::$listener = Listener::get_instance();
 	}
 
 	static function initialize_sender() {
-		require_once dirname( __FILE__ ) . '/class.jetpack-sync-sender.php';
-		self::$sender = Jetpack_Sync_Sender::get_instance();
+		self::$sender = Sender::get_instance();
 
 		// bind the sending process
 		add_filter( 'jetpack_sync_send_data', array( __CLASS__, 'send_data' ), 10, 6 );
 	}
 
 	static function initialize_woocommerce() {
-		if ( false === class_exists( 'WooCommerce' ) ) {
+		if ( false === class_exists( '\\WooCommerce' ) ) {
 			return;
 		}
-		add_filter( 'jetpack_sync_modules', array( 'Jetpack_Sync_Actions', 'add_woocommerce_sync_module' ) );
+		add_filter( 'jetpack_sync_modules', array( 'Actions', 'add_woocommerce_sync_module' ) );
 	}
 
 	static function add_woocommerce_sync_module( $sync_modules ) {
-		require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-woocommerce.php';
-		$sync_modules[] = 'Jetpack_Sync_Module_WooCommerce';
+		$sync_modules[] = 'Module_WooCommerce';
 		return $sync_modules;
 	}
 
@@ -343,12 +333,11 @@ static function initialize_wp_super_cache() {
 		if ( false === function_exists( 'wp_cache_is_enabled' ) ) {
 			return;
 		}
-		add_filter( 'jetpack_sync_modules', array( 'Jetpack_Sync_Actions', 'add_wp_super_cache_sync_module' ) );
+		add_filter( 'jetpack_sync_modules', array( 'Actions', 'add_wp_super_cache_sync_module' ) );
 	}
 
 	static function add_wp_super_cache_sync_module( $sync_modules ) {
-		require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-wp-super-cache.php';
-		$sync_modules[] = 'Jetpack_Sync_Module_WP_Super_Cache';
+		$sync_modules[] = 'Module_WP_Super_Cache';
 		return $sync_modules;
 	}
 
@@ -445,11 +434,10 @@ static function cleanup_on_upgrade( $new_version = null, $old_version = null ) {
 
 		$is_new_sync_upgrade = version_compare( $old_version, '4.2', '>=' );
 		if ( ! empty( $old_version ) && $is_new_sync_upgrade && version_compare( $old_version, '4.5', '<' ) ) {
-			require_once dirname( __FILE__ ) . '/class.jetpack-sync-settings.php';
 			self::clear_sync_cron_jobs();
-			Jetpack_Sync_Settings::update_settings(
+			Settings::update_settings(
 				array(
-					'render_filtered_content' => Jetpack_Sync_Defaults::$default_render_filtered_content,
+					'render_filtered_content' => Defaults::$default_render_filtered_content,
 				)
 			);
 		}
@@ -464,7 +452,7 @@ static function cleanup_on_upgrade( $new_version = null, $old_version = null ) {
 	static function get_sync_status( $fields = null ) {
 		self::initialize_sender();
 
-		$sync_module     = Jetpack_Sync_Modules::get_module( 'full-sync' );
+		$sync_module     = Modules::get_module( 'full-sync' );
 		$queue           = self::$sender->get_sync_queue();
 		$full_queue      = self::$sender->get_full_sync_queue();
 		$cron_timestamps = array_keys( _get_cron_array() );
@@ -473,8 +461,7 @@ static function get_sync_status( $fields = null ) {
 		$checksums = array();
 
 		if ( ! empty( $fields ) ) {
-			require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-wp-replicastore.php';
-			$store         = new Jetpack_Sync_WP_Replicastore();
+			$store         = new WP_Replicastore();
 			$fields_params = array_map( 'trim', explode( ',', $fields ) );
 
 			if ( in_array( 'posts_checksum', $fields_params, true ) ) {
@@ -511,19 +498,19 @@ static function get_sync_status( $fields = null ) {
 }
 
 // Check for WooCommerce support
-add_action( 'plugins_loaded', array( 'Jetpack_Sync_Actions', 'initialize_woocommerce' ), 5 );
+add_action( 'plugins_loaded', array( 'Actions', 'initialize_woocommerce' ), 5 );
 
 // Check for WP Super Cache
-add_action( 'plugins_loaded', array( 'Jetpack_Sync_Actions', 'initialize_wp_super_cache' ), 5 );
+add_action( 'plugins_loaded', array( 'Actions', 'initialize_wp_super_cache' ), 5 );
 
 /*
  * Init after plugins loaded and before the `init` action. This helps with issues where plugins init
  * with a high priority or sites that use alternate cron.
  */
-add_action( 'plugins_loaded', array( 'Jetpack_Sync_Actions', 'init' ), 90 );
+add_action( 'plugins_loaded', array( 'Actions', 'init' ), 90 );
 
 
 
 // We need to define this here so that it's hooked before `updating_jetpack_version` is called
-add_action( 'updating_jetpack_version', array( 'Jetpack_Sync_Actions', 'cleanup_on_upgrade' ), 10, 2 );
-add_action( 'jetpack_user_authorized', array( 'Jetpack_Sync_Actions', 'do_initial_sync' ), 10, 0 );
+add_action( 'updating_jetpack_version', array( 'Actions', 'cleanup_on_upgrade' ), 10, 2 );
+add_action( 'jetpack_user_authorized', array( 'Actions', 'do_initial_sync' ), 10, 0 );
diff --git a/sync/interface.jetpack-sync-codec.php b/packages/sync/src/Codec.php
similarity index 86%
rename from sync/interface.jetpack-sync-codec.php
rename to packages/sync/src/Codec.php
index 1405d90c63b7..d0637989041c 100644
--- a/sync/interface.jetpack-sync-codec.php
+++ b/packages/sync/src/Codec.php
@@ -1,10 +1,12 @@
 <?php
 
+namespace Automattic\Jetpack\Sync;
+
 /**
  * Very simple interface for encoding and decoding input
  * This is used to provide compression and serialization to messages
  **/
-interface iJetpack_Sync_Codec {
+interface Codec {
 	// we send this with the payload so we can select the appropriate decoder at the other end
 	public function name();
 
diff --git a/sync/class.jetpack-sync-defaults.php b/packages/sync/src/Defaults.php
similarity index 81%
rename from sync/class.jetpack-sync-defaults.php
rename to packages/sync/src/Defaults.php
index 4390d665f0d5..27d5cb559b3f 100644
--- a/sync/class.jetpack-sync-defaults.php
+++ b/packages/sync/src/Defaults.php
@@ -1,10 +1,13 @@
 <?php
+
+namespace Automattic\Jetpack\Sync;
+
 require_once JETPACK__PLUGIN_DIR . 'modules/sso/class.jetpack-sso-helpers.php';
 
 /**
  * Just some defaults that we share with the server
  */
-class Jetpack_Sync_Defaults {
+class Defaults {
 
 	static $default_options_whitelist = array(
 		'stylesheet',
@@ -217,39 +220,39 @@ public static function get_constants_whitelist() {
 	}
 
 	static $default_callable_whitelist = array(
-		'wp_max_upload_size'               => 'wp_max_upload_size',
-		'is_main_network'                  => array( 'Jetpack', 'is_multi_network' ),
-		'is_multi_site'                    => 'is_multisite',
-		'main_network_site'                => array( 'Jetpack_Sync_Functions', 'main_network_site_url' ),
-		'site_url'                         => array( 'Jetpack_Sync_Functions', 'site_url' ),
-		'home_url'                         => array( 'Jetpack_Sync_Functions', 'home_url' ),
-		'single_user_site'                 => array( 'Jetpack', 'is_single_user_site' ),
-		'updates'                          => array( 'Jetpack', 'get_updates' ),
-		'has_file_system_write_access'     => array( 'Jetpack_Sync_Functions', 'file_system_write_access' ),
-		'is_version_controlled'            => array( 'Jetpack_Sync_Functions', 'is_version_controlled' ),
-		'taxonomies'                       => array( 'Jetpack_Sync_Functions', 'get_taxonomies' ),
-		'post_types'                       => array( 'Jetpack_Sync_Functions', 'get_post_types' ),
-		'post_type_features'               => array( 'Jetpack_Sync_Functions', 'get_post_type_features' ),
-		'shortcodes'                       => array( 'Jetpack_Sync_Functions', 'get_shortcodes' ),
-		'rest_api_allowed_post_types'      => array( 'Jetpack_Sync_Functions', 'rest_api_allowed_post_types' ),
-		'rest_api_allowed_public_metadata' => array( 'Jetpack_Sync_Functions', 'rest_api_allowed_public_metadata' ),
-		'sso_is_two_step_required'         => array( 'Jetpack_SSO_Helpers', 'is_two_step_required' ),
-		'sso_should_hide_login_form'       => array( 'Jetpack_SSO_Helpers', 'should_hide_login_form' ),
-		'sso_match_by_email'               => array( 'Jetpack_SSO_Helpers', 'match_by_email' ),
-		'sso_new_user_override'            => array( 'Jetpack_SSO_Helpers', 'new_user_override' ),
-		'sso_bypass_default_login_form'    => array( 'Jetpack_SSO_Helpers', 'bypass_login_forward_wpcom' ),
-		'wp_version'                       => array( 'Jetpack_Sync_Functions', 'wp_version' ),
-		'get_plugins'                      => array( 'Jetpack_Sync_Functions', 'get_plugins' ),
-		'get_plugins_action_links'         => array( 'Jetpack_Sync_functions', 'get_plugins_action_links' ),
-		'active_modules'                   => array( 'Jetpack', 'get_active_modules' ),
-		'hosting_provider'                 => array( 'Jetpack_Sync_Functions', 'get_hosting_provider' ),
-		'locale'                           => 'get_locale',
-		'site_icon_url'                    => array( 'Jetpack_Sync_Functions', 'site_icon_url' ),
-		'roles'                            => array( 'Jetpack_Sync_Functions', 'roles' ),
-		'timezone'                         => array( 'Jetpack_Sync_Functions', 'get_timezone' ),
-		'available_jetpack_blocks'         => array( 'Jetpack_Gutenberg', 'get_availability' ), // Includes both Gutenberg blocks *and* plugins
-		'paused_themes'                    => array( 'Jetpack_Sync_Functions', 'get_paused_themes' ),
-		'paused_plugins'                   => array( 'Jetpack_Sync_Functions', 'get_paused_plugins' ),
+		'wp_max_upload_size'               => '\\wp_max_upload_size',
+		'is_main_network'                  => array( '\\Jetpack', 'is_multi_network' ),
+		'is_multi_site'                    => '\\is_multisite',
+		'main_network_site'                => array( __NAMESPACE__ . '\\Functions', 'main_network_site_url' ),
+		'site_url'                         => array( __NAMESPACE__ . '\\Functions', 'site_url' ),
+		'home_url'                         => array( __NAMESPACE__ . '\\Functions', 'home_url' ),
+		'single_user_site'                 => array( '\\Jetpack', 'is_single_user_site' ),
+		'updates'                          => array( '\\Jetpack', 'get_updates' ),
+		'has_file_system_write_access'     => array( __NAMESPACE__ . '\\Functions', 'file_system_write_access' ),
+		'is_version_controlled'            => array( __NAMESPACE__ . '\\Functions', 'is_version_controlled' ),
+		'taxonomies'                       => array( __NAMESPACE__ . '\\Functions', 'get_taxonomies' ),
+		'post_types'                       => array( __NAMESPACE__ . '\\Functions', 'get_post_types' ),
+		'post_type_features'               => array( __NAMESPACE__ . '\\Functions', 'get_post_type_features' ),
+		'shortcodes'                       => array( __NAMESPACE__ . '\\Functions', 'get_shortcodes' ),
+		'rest_api_allowed_post_types'      => array( __NAMESPACE__ . '\\Functions', 'rest_api_allowed_post_types' ),
+		'rest_api_allowed_public_metadata' => array( __NAMESPACE__ . '\\Functions', 'rest_api_allowed_public_metadata' ),
+		'sso_is_two_step_required'         => array( '\\Jetpack_SSO_Helpers', 'is_two_step_required' ),
+		'sso_should_hide_login_form'       => array( '\\Jetpack_SSO_Helpers', 'should_hide_login_form' ),
+		'sso_match_by_email'               => array( '\\Jetpack_SSO_Helpers', 'match_by_email' ),
+		'sso_new_user_override'            => array( '\\Jetpack_SSO_Helpers', 'new_user_override' ),
+		'sso_bypass_default_login_form'    => array( '\\Jetpack_SSO_Helpers', 'bypass_login_forward_wpcom' ),
+		'wp_version'                       => array( __NAMESPACE__ . '\\Functions', 'wp_version' ),
+		'get_plugins'                      => array( __NAMESPACE__ . '\\Functions', 'get_plugins' ),
+		'get_plugins_action_links'         => array( __NAMESPACE__ . '\\Functions', 'get_plugins_action_links' ),
+		'active_modules'                   => array( '\\Jetpack', 'get_active_modules' ),
+		'hosting_provider'                 => array( __NAMESPACE__ . '\\Functions', 'get_hosting_provider' ),
+		'locale'                           => '\\get_locale',
+		'site_icon_url'                    => array( __NAMESPACE__ . '\\Functions', 'site_icon_url' ),
+		'roles'                            => array( __NAMESPACE__ . '\\Functions', 'roles' ),
+		'timezone'                         => array( __NAMESPACE__ . '\\Functions', 'get_timezone' ),
+		'available_jetpack_blocks'         => array( '\\Jetpack_Gutenberg', 'get_availability' ), // Includes both Gutenberg blocks *and* plugins
+		'paused_themes'                    => array( __NAMESPACE__ . '\\Functions', 'get_paused_themes' ),
+		'paused_plugins'                   => array( __NAMESPACE__ . '\\Functions', 'get_paused_plugins' ),
 	);
 
 
@@ -352,12 +355,12 @@ public static function get_callable_whitelist() {
 	);
 
 	static $default_multisite_callable_whitelist = array(
-		'network_name'                        => array( 'Jetpack', 'network_name' ),
-		'network_allow_new_registrations'     => array( 'Jetpack', 'network_allow_new_registrations' ),
-		'network_add_new_users'               => array( 'Jetpack', 'network_add_new_users' ),
-		'network_site_upload_space'           => array( 'Jetpack', 'network_site_upload_space' ),
-		'network_upload_file_types'           => array( 'Jetpack', 'network_upload_file_types' ),
-		'network_enable_administration_menus' => array( 'Jetpack', 'network_enable_administration_menus' ),
+		'network_name'                        => array( '\\Jetpack', 'network_name' ),
+		'network_allow_new_registrations'     => array( '\\Jetpack', 'network_allow_new_registrations' ),
+		'network_add_new_users'               => array( '\\Jetpack', 'network_add_new_users' ),
+		'network_site_upload_space'           => array( '\\Jetpack', 'network_site_upload_space' ),
+		'network_upload_file_types'           => array( '\\Jetpack', 'network_upload_file_types' ),
+		'network_enable_administration_menus' => array( '\\Jetpack', 'network_enable_administration_menus' ),
 	);
 
 	public static function get_multisite_callable_whitelist() {
@@ -562,7 +565,7 @@ static function get_max_sync_execution_time() {
 
 	static function get_default_setting( $setting ) {
 		$default_name = "default_$setting"; // e.g. default_dequeue_max_bytes
-		return Jetpack_Sync_Defaults::$$default_name;
+		return self::$$default_name;
 	}
 
 	static $default_network_options_whitelist = array(
diff --git a/sync/class.jetpack-sync-functions.php b/packages/sync/src/Functions.php
similarity index 94%
rename from sync/class.jetpack-sync-functions.php
rename to packages/sync/src/Functions.php
index efae4bf89a4c..0ebb42d0c41f 100644
--- a/sync/class.jetpack-sync-functions.php
+++ b/packages/sync/src/Functions.php
@@ -1,10 +1,12 @@
 <?php
 
+namespace Automattic\Jetpack\Sync;
+
 /*
  * Utility functions to generate data synced to wpcom
  */
 
-class Jetpack_Sync_Functions {
+class Functions {
 	const HTTPS_CHECK_OPTION_PREFIX = 'jetpack_sync_https_history_';
 	const HTTPS_CHECK_HISTORY       = 5;
 
@@ -81,7 +83,7 @@ public static function get_post_types() {
 	public static function sanitize_post_type( $post_type ) {
 		// Lets clone the post type object instead of modifing the global one.
 		$sanitized_post_type = array();
-		foreach ( Jetpack_Sync_Defaults::$default_post_type_attributes as $attribute_key => $default_value ) {
+		foreach ( Defaults::$default_post_type_attributes as $attribute_key => $default_value ) {
 			if ( isset( $post_type->{ $attribute_key } ) ) {
 				$sanitized_post_type[ $attribute_key ] = $post_type->{ $attribute_key };
 			}
@@ -91,7 +93,7 @@ public static function sanitize_post_type( $post_type ) {
 
 	public static function expand_synced_post_type( $sanitized_post_type, $post_type ) {
 		$post_type        = sanitize_key( $post_type );
-		$post_type_object = new WP_Post_Type( $post_type, $sanitized_post_type );
+		$post_type_object = new \WP_Post_Type( $post_type, $sanitized_post_type );
 		$post_type_object->add_supports();
 		$post_type_object->add_rewrite_rules();
 		$post_type_object->add_hooks();
@@ -141,10 +143,10 @@ public static function rest_api_allowed_public_metadata() {
 	 **/
 	public static function is_version_controlled() {
 
-		if ( ! class_exists( 'WP_Automatic_Updater' ) ) {
+		if ( ! class_exists( '\\WP_Automatic_Updater' ) ) {
 			require_once ABSPATH . 'wp-admin/includes/class-wp-upgrader.php';
 		}
-		$updater = new WP_Automatic_Updater();
+		$updater = new \WP_Automatic_Updater();
 
 		return (bool) strval( $updater->is_vcs_checkout( $context = ABSPATH ) );
 	}
@@ -193,8 +195,8 @@ public static function get_raw_or_filtered_url( $url_type ) {
 			: 'site_url';
 
 		if (
-			! Jetpack_Constants::is_defined( 'JETPACK_SYNC_USE_RAW_URL' ) ||
-			Jetpack_Constants::get_constant( 'JETPACK_SYNC_USE_RAW_URL' )
+			! \Jetpack_Constants::is_defined( 'JETPACK_SYNC_USE_RAW_URL' ) ||
+			\Jetpack_Constants::get_constant( 'JETPACK_SYNC_USE_RAW_URL' )
 		) {
 			$scheme = is_ssl() ? 'https' : 'http';
 			$url    = self::get_raw_url( $url_type );
@@ -269,12 +271,12 @@ public static function get_raw_url( $option_name ) {
 
 		// Since we disregard the constant for multisites in ms-default-filters.php,
 		// let's also use the db value if this is a multisite.
-		if ( ! is_multisite() && Jetpack_Constants::is_defined( $constant ) ) {
-			$value = Jetpack_Constants::get_constant( $constant );
+		if ( ! is_multisite() && \Jetpack_Constants::is_defined( $constant ) ) {
+			$value = \Jetpack_Constants::get_constant( $constant );
 		} else {
 			// Let's get the option from the database so that we can bypass filters. This will help
 			// ensure that we get more uniform values.
-			$value = Jetpack_Options::get_raw_option( $option_name );
+			$value = \Jetpack_Options::get_raw_option( $option_name );
 		}
 
 		return $value;
@@ -326,7 +328,7 @@ public static function get_plugins() {
 	 */
 	public static function get_plugins_action_links( $plugin_file_singular = null ) {
 		// Some sites may have DOM disabled in PHP fail early
-		if ( ! class_exists( 'DOMDocument' ) ) {
+		if ( ! class_exists( '\\DOMDocument' ) ) {
 			return array();
 		}
 		$plugins_action_links = get_option( 'jetpack_plugin_api_action_links', array() );
diff --git a/sync/class.jetpack-sync-json-deflate-array-codec.php b/packages/sync/src/JSON_Deflate_Array_Codec.php
similarity index 88%
rename from sync/class.jetpack-sync-json-deflate-array-codec.php
rename to packages/sync/src/JSON_Deflate_Array_Codec.php
index 04d3dd7df181..7cced0022e83 100644
--- a/sync/class.jetpack-sync-json-deflate-array-codec.php
+++ b/packages/sync/src/JSON_Deflate_Array_Codec.php
@@ -1,12 +1,12 @@
 <?php
 
-require_once dirname( __FILE__ ) . '/interface.jetpack-sync-codec.php';
+namespace Automattic\Jetpack\Sync;
 
 /**
- * An implementation of iJetpack_Sync_Codec that uses gzip's DEFLATE
+ * An implementation of Codec that uses gzip's DEFLATE
  * algorithm to compress objects serialized using json_encode
  */
-class Jetpack_Sync_JSON_Deflate_Array_Codec implements iJetpack_Sync_Codec {
+class JSON_Deflate_Array_Codec implements Codec {
 	const CODEC_NAME = 'deflate-json-array';
 
 	public function name() {
diff --git a/sync/class.jetpack-sync-listener.php b/packages/sync/src/Listener.php
similarity index 87%
rename from sync/class.jetpack-sync-listener.php
rename to packages/sync/src/Listener.php
index 62abc0d26802..39d0f915b0db 100644
--- a/sync/class.jetpack-sync-listener.php
+++ b/packages/sync/src/Listener.php
@@ -1,14 +1,11 @@
 <?php
 
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-settings.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-queue.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-modules.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-actions.php';
+namespace Automattic\Jetpack\Sync;
 
 /**
  * This class monitors actions and logs them to the queue to be sent
  */
-class Jetpack_Sync_Listener {
+class Listener {
 	const QUEUE_STATE_CHECK_TRANSIENT = 'jetpack_sync_last_checked_queue_state';
 	const QUEUE_STATE_CHECK_TIMEOUT   = 300; // 5 minutes
 
@@ -38,7 +35,7 @@ private function init() {
 		$handler           = array( $this, 'action_handler' );
 		$full_sync_handler = array( $this, 'full_sync_action_handler' );
 
-		foreach ( Jetpack_Sync_Modules::get_modules() as $module ) {
+		foreach ( Modules::get_modules() as $module ) {
 			$module->init_listeners( $handler );
 			$module->init_full_sync_listeners( $full_sync_handler );
 		}
@@ -86,7 +83,7 @@ function force_recheck_queue_limit() {
 	// prevent adding items to the queue if it hasn't sent an item for 15 mins
 	// AND the queue is over 1000 items long (by default)
 	function can_add_to_queue( $queue ) {
-		if ( ! Jetpack_Sync_Settings::is_sync_enabled() ) {
+		if ( ! Settings::is_sync_enabled() ) {
 			return false;
 		}
 
@@ -142,12 +139,11 @@ function bulk_enqueue_full_sync_actions( $action_name, $args_array ) {
 		$data_to_enqueue = array();
 		$user_id         = get_current_user_id();
 		$currtime        = microtime( true );
-		$is_importing    = Jetpack_Sync_Settings::is_importing();
+		$is_importing    = Settings::is_importing();
 
 		foreach ( $args_array as $args ) {
 			$previous_end = isset( $args['previous_end'] ) ? $args['previous_end'] : null;
-			$args = isset( $args['ids'] ) ? $args['ids'] : $args;
-
+			$args         = isset( $args['ids'] ) ? $args['ids'] : $args;
 
 			/**
 			 * Modify or reject the data within an action before it is enqueued locally.
@@ -158,7 +154,7 @@ function bulk_enqueue_full_sync_actions( $action_name, $args_array ) {
 			 *
 			 * @param array The action parameters
 			 */
-			$args = apply_filters( "jetpack_sync_before_enqueue_$action_name", $args );
+			$args        = apply_filters( "jetpack_sync_before_enqueue_$action_name", $args );
 			$action_data = array( $args );
 			if ( ! is_null( $previous_end ) ) {
 				$action_data[] = $previous_end;
@@ -182,7 +178,7 @@ function bulk_enqueue_full_sync_actions( $action_name, $args_array ) {
 
 	function enqueue_action( $current_filter, $args, $queue ) {
 		// don't enqueue an action during the outbound http request - this prevents recursion
-		if ( Jetpack_Sync_Settings::is_sending() ) {
+		if ( Settings::is_sending() ) {
 			return;
 		}
 
@@ -238,7 +234,7 @@ function enqueue_action( $current_filter, $args, $queue ) {
 					$args,
 					get_current_user_id(),
 					microtime( true ),
-					Jetpack_Sync_Settings::is_importing(),
+					Settings::is_importing(),
 					$this->get_actor( $current_filter, $args ),
 				)
 			);
@@ -249,16 +245,16 @@ function enqueue_action( $current_filter, $args, $queue ) {
 					$args,
 					get_current_user_id(),
 					microtime( true ),
-					Jetpack_Sync_Settings::is_importing(),
+					Settings::is_importing(),
 				)
 			);
 		}
 
 		// since we've added some items, let's try to load the sender so we can send them as quickly as possible
-		if ( ! Jetpack_Sync_Actions::$sender ) {
+		if ( ! Actions::$sender ) {
 			add_filter( 'jetpack_sync_sender_should_load', '__return_true' );
 			if ( did_action( 'init' ) ) {
-				Jetpack_Sync_Actions::add_sender_shutdown();
+				Actions::add_sender_shutdown();
 			}
 		}
 	}
@@ -270,7 +266,7 @@ function get_actor( $current_filter, $args ) {
 			$user = wp_get_current_user();
 		}
 
-		$translated_role = Jetpack::translate_user_to_role( $user );
+		$translated_role = \Jetpack::translate_user_to_role( $user );
 
 		$actor = array(
 			'wpcom_user_id'    => null,
@@ -314,10 +310,10 @@ function should_send_user_data_with_actor( $current_filter ) {
 	}
 
 	function set_defaults() {
-		$this->sync_queue      = new Jetpack_Sync_Queue( 'sync' );
-		$this->full_sync_queue = new Jetpack_Sync_Queue( 'full_sync' );
-		$this->set_queue_size_limit( Jetpack_Sync_Settings::get_setting( 'max_queue_size' ) );
-		$this->set_queue_lag_limit( Jetpack_Sync_Settings::get_setting( 'max_queue_lag' ) );
+		$this->sync_queue      = new Queue( 'sync' );
+		$this->full_sync_queue = new Queue( 'full_sync' );
+		$this->set_queue_size_limit( Settings::get_setting( 'max_queue_size' ) );
+		$this->set_queue_lag_limit( Settings::get_setting( 'max_queue_lag' ) );
 	}
 
 	function get_request_url() {
diff --git a/sync/class.jetpack-sync-module.php b/packages/sync/src/Module.php
similarity index 97%
rename from sync/class.jetpack-sync-module.php
rename to packages/sync/src/Module.php
index b3fbe8685915..3684082c85e0 100644
--- a/sync/class.jetpack-sync-module.php
+++ b/packages/sync/src/Module.php
@@ -1,9 +1,11 @@
 <?php
 
+namespace Automattic\Jetpack\Sync;
+
 /**
  * Basic methods implemented by Jetpack Sync extensions
  */
-abstract class Jetpack_Sync_Module {
+abstract class Module {
 	const ARRAY_CHUNK_SIZE = 10;
 
 	abstract public function name();
@@ -69,7 +71,7 @@ protected function enqueue_all_ids_as_action( $action_name, $table_name, $id_fie
 		$page                  = 1;
 		$chunk_count           = 0;
 		$previous_interval_end = $state ? $state : '~0';
-		$listener              = Jetpack_Sync_Listener::get_instance();
+		$listener              = Listener::get_instance();
 
 		// count down from max_id to min_id so we get newest posts/comments/etc first
 		while ( $ids = $wpdb->get_col( "SELECT {$id_field} FROM {$table_name} WHERE {$where_sql} AND {$id_field} < {$previous_interval_end} ORDER BY {$id_field} DESC LIMIT {$items_per_page}" ) ) {
diff --git a/sync/class.jetpack-sync-module-attachments.php b/packages/sync/src/Module_Attachments.php
similarity index 95%
rename from sync/class.jetpack-sync-module-attachments.php
rename to packages/sync/src/Module_Attachments.php
index f68ba8328a6a..f581c4f73f6a 100644
--- a/sync/class.jetpack-sync-module-attachments.php
+++ b/packages/sync/src/Module_Attachments.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_Attachments extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_Attachments extends Module {
 	function name() {
 		return 'attachments';
 	}
diff --git a/sync/class.jetpack-sync-module-callables.php b/packages/sync/src/Module_Callables.php
similarity index 87%
rename from sync/class.jetpack-sync-module-callables.php
rename to packages/sync/src/Module_Callables.php
index d46d5514bb31..764c15431537 100644
--- a/sync/class.jetpack-sync-module-callables.php
+++ b/packages/sync/src/Module_Callables.php
@@ -1,8 +1,8 @@
 <?php
 
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-functions.php';
+namespace Automattic\Jetpack\Sync;
 
-class Jetpack_Sync_Module_Callables extends Jetpack_Sync_Module {
+class Module_Callables extends Module {
 	const CALLABLES_CHECKSUM_OPTION_NAME = 'jetpack_callables_sync_checksum';
 	const CALLABLES_AWAIT_TRANSIENT_NAME = 'jetpack_sync_callables_await';
 
@@ -14,9 +14,9 @@ public function name() {
 
 	public function set_defaults() {
 		if ( is_multisite() ) {
-			$this->callable_whitelist = array_merge( Jetpack_Sync_Defaults::get_callable_whitelist(), Jetpack_Sync_Defaults::get_multisite_callable_whitelist() );
+			$this->callable_whitelist = array_merge( Defaults::get_callable_whitelist(), Defaults::get_multisite_callable_whitelist() );
 		} else {
-			$this->callable_whitelist = Jetpack_Sync_Defaults::get_callable_whitelist();
+			$this->callable_whitelist = Defaults::get_callable_whitelist();
 		}
 	}
 
@@ -65,7 +65,7 @@ public function reset_data() {
 
 		$url_callables = array( 'home_url', 'site_url', 'main_network_site_url' );
 		foreach ( $url_callables as $callable ) {
-			delete_option( Jetpack_Sync_Functions::HTTPS_CHECK_OPTION_PREFIX . $callable );
+			delete_option( Functions::HTTPS_CHECK_OPTION_PREFIX . $callable );
 		}
 	}
 
@@ -80,7 +80,7 @@ function get_callable_whitelist() {
 	public function get_all_callables() {
 		// get_all_callables should run as the master user always.
 		$current_user_id = get_current_user_id();
-		wp_set_current_user( Jetpack_Options::get_option( 'master_user' ) );
+		wp_set_current_user( \Jetpack_Options::get_option( 'master_user' ) );
 		$callables = array_combine(
 			array_keys( $this->get_callable_whitelist() ),
 			array_map( array( $this, 'get_callable' ), array_values( $this->get_callable_whitelist() ) )
@@ -127,7 +127,7 @@ public function unlock_plugin_action_link_and_callables() {
 
 	public function set_plugin_action_links() {
 		if (
-			! class_exists( 'DOMDocument' ) ||
+			! class_exists( '\\DOMDocument' ) ||
 			! function_exists( 'libxml_use_internal_errors' ) ||
 			! function_exists( 'mb_convert_encoding' )
 		) {
@@ -142,7 +142,7 @@ public function set_plugin_action_links() {
 		if ( ! empty( $plugins_lock ) && ( isset( $current_screeen->id ) && $current_screeen->id !== 'plugins' ) ) {
 			return;
 		}
-		$plugins = array_keys( Jetpack_Sync_Functions::get_plugins() );
+		$plugins = array_keys( Functions::get_plugins() );
 		foreach ( $plugins as $plugin_file ) {
 			/**
 			 *  Plugins often like to unset things but things break if they are not able to.
@@ -203,7 +203,7 @@ public function should_send_callable( $callable_checksums, $name, $checksum ) {
 			'home_url',
 			'site_url',
 		);
-		if ( in_array( $name, $idc_override_callables ) && Jetpack_Options::get_option( 'migrate_for_idc' ) ) {
+		if ( in_array( $name, $idc_override_callables ) && \Jetpack_Options::get_option( 'migrate_for_idc' ) ) {
 			return true;
 		}
 
@@ -212,7 +212,7 @@ public function should_send_callable( $callable_checksums, $name, $checksum ) {
 
 	public function maybe_sync_callables() {
 		if ( ! apply_filters( 'jetpack_check_and_send_callables', false ) ) {
-			if ( ! is_admin() || Jetpack_Sync_Settings::is_doing_cron() ) {
+			if ( ! is_admin() || Settings::is_doing_cron() ) {
 				return;
 			}
 
@@ -221,7 +221,7 @@ public function maybe_sync_callables() {
 			}
 		}
 
-		set_transient( self::CALLABLES_AWAIT_TRANSIENT_NAME, microtime( true ), Jetpack_Sync_Defaults::$default_sync_callables_wait_time );
+		set_transient( self::CALLABLES_AWAIT_TRANSIENT_NAME, microtime( true ), Defaults::$default_sync_callables_wait_time );
 
 		$callables = $this->get_all_callables();
 
@@ -229,8 +229,8 @@ public function maybe_sync_callables() {
 			return;
 		}
 
-		$callable_checksums = (array) Jetpack_Options::get_raw_option( self::CALLABLES_CHECKSUM_OPTION_NAME, array() );
-		$has_changed = false;
+		$callable_checksums = (array) \Jetpack_Options::get_raw_option( self::CALLABLES_CHECKSUM_OPTION_NAME, array() );
+		$has_changed        = false;
 		// only send the callables that have changed
 		foreach ( $callables as $name => $value ) {
 			$checksum = $this->get_check_sum( $value );
@@ -246,13 +246,13 @@ public function maybe_sync_callables() {
 				 */
 				do_action( 'jetpack_sync_callable', $name, $value );
 				$callable_checksums[ $name ] = $checksum;
-				$has_changed = true;
+				$has_changed                 = true;
 			} else {
 				$callable_checksums[ $name ] = $checksum;
 			}
 		}
 		if ( $has_changed ) {
-			Jetpack_Options::update_raw_option( self::CALLABLES_CHECKSUM_OPTION_NAME, $callable_checksums );
+			\Jetpack_Options::update_raw_option( self::CALLABLES_CHECKSUM_OPTION_NAME, $callable_checksums );
 		}
 
 	}
@@ -264,7 +264,7 @@ public function expand_callables( $args ) {
 			foreach ( $callables as $name => $value ) {
 				$callables_checksums[ $name ] = $this->get_check_sum( $value );
 			}
-			Jetpack_Options::update_raw_option( self::CALLABLES_CHECKSUM_OPTION_NAME, $callables_checksums );
+			\Jetpack_Options::update_raw_option( self::CALLABLES_CHECKSUM_OPTION_NAME, $callables_checksums );
 			return $callables;
 		}
 
diff --git a/sync/class.jetpack-sync-module-comments.php b/packages/sync/src/Module_Comments.php
similarity index 95%
rename from sync/class.jetpack-sync-module-comments.php
rename to packages/sync/src/Module_Comments.php
index 0a0ee16f1c59..64bb3c6e0027 100644
--- a/sync/class.jetpack-sync-module-comments.php
+++ b/packages/sync/src/Module_Comments.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_Comments extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_Comments extends Module {
 
 	public function name() {
 		return 'comments';
@@ -169,7 +171,7 @@ function filter_comment( $comment ) {
 
 	// Comment Meta
 	function is_whitelisted_comment_meta( $meta_key ) {
-		return in_array( $meta_key, Jetpack_Sync_Settings::get_setting( 'comment_meta_whitelist' ) );
+		return in_array( $meta_key, Settings::get_setting( 'comment_meta_whitelist' ) );
 	}
 
 	function filter_meta( $args ) {
@@ -189,7 +191,7 @@ public function expand_comment_ids( $args ) {
 
 		return array(
 			$comments,
-			$this->get_metadata( $comment_ids, 'comment', Jetpack_Sync_Settings::get_setting( 'comment_meta_whitelist' ) ),
+			$this->get_metadata( $comment_ids, 'comment', Settings::get_setting( 'comment_meta_whitelist' ) ),
 			$previous_interval_end,
 		);
 	}
diff --git a/sync/class.jetpack-sync-module-constants.php b/packages/sync/src/Module_Constants.php
similarity index 92%
rename from sync/class.jetpack-sync-module-constants.php
rename to packages/sync/src/Module_Constants.php
index f3af31951ce2..f73248682fbc 100644
--- a/sync/class.jetpack-sync-module-constants.php
+++ b/packages/sync/src/Module_Constants.php
@@ -1,8 +1,8 @@
 <?php
 
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-defaults.php';
+namespace Automattic\Jetpack\Sync;
 
-class Jetpack_Sync_Module_Constants extends Jetpack_Sync_Module {
+class Module_Constants extends Module {
 	const CONSTANTS_CHECKSUM_OPTION_NAME = 'jetpack_constants_sync_checksum';
 	const CONSTANTS_AWAIT_TRANSIENT_NAME = 'jetpack_sync_constants_await';
 
@@ -35,7 +35,7 @@ function set_constants_whitelist( $constants ) {
 	}
 
 	function get_constants_whitelist() {
-		return Jetpack_Sync_Defaults::get_constants_whitelist();
+		return Defaults::get_constants_whitelist();
 	}
 
 	function enqueue_full_sync_actions( $config, $max_items_to_enqueue, $state ) {
@@ -65,7 +65,7 @@ function maybe_sync_constants() {
 			return;
 		}
 
-		set_transient( self::CONSTANTS_AWAIT_TRANSIENT_NAME, microtime( true ), Jetpack_Sync_Defaults::$default_sync_constants_wait_time );
+		set_transient( self::CONSTANTS_AWAIT_TRANSIENT_NAME, microtime( true ), Defaults::$default_sync_constants_wait_time );
 
 		$constants = $this->get_all_constants();
 		if ( empty( $constants ) ) {
diff --git a/sync/class.jetpack-sync-module-full-sync.php b/packages/sync/src/Module_Full_Sync.php
similarity index 83%
rename from sync/class.jetpack-sync-module-full-sync.php
rename to packages/sync/src/Module_Full_Sync.php
index c50b6df74c0e..ab241da892d7 100644
--- a/sync/class.jetpack-sync-module-full-sync.php
+++ b/packages/sync/src/Module_Full_Sync.php
@@ -1,18 +1,20 @@
 <?php
 
+namespace Automattic\Jetpack\Sync;
+
 /**
  * This class does a full resync of the database by
  * enqueuing an outbound action for every single object
  * that we care about.
  *
- * This class, and its related class Jetpack_Sync_Module, contain a few non-obvious optimisations that should be explained:
+ * This class, and its related class Module, contain a few non-obvious optimisations that should be explained:
  * - we fire an action called jetpack_full_sync_start so that WPCOM can erase the contents of the cached database
  * - for each object type, we page through the object IDs and enqueue them by firing some monitored actions
- * - we load the full objects for those IDs in chunks of Jetpack_Sync_Module::ARRAY_CHUNK_SIZE (to reduce the number of MySQL calls)
- * - we fire a trigger for the entire array which the Jetpack_Sync_Listener then serializes and queues.
+ * - we load the full objects for those IDs in chunks of Module::ARRAY_CHUNK_SIZE (to reduce the number of MySQL calls)
+ * - we fire a trigger for the entire array which the Listener then serializes and queues.
  */
 
-class Jetpack_Sync_Module_Full_Sync extends Jetpack_Sync_Module {
+class Module_Full_Sync extends Module {
 	const STATUS_OPTION_PREFIX = 'jetpack_sync_full_';
 	const FULL_SYNC_TIMEOUT    = 3600;
 
@@ -52,19 +54,19 @@ function start( $module_configs = null ) {
 
 		$enqueue_status   = array();
 		$full_sync_config = array();
-		$include_empty = false;
-		$empty = array();
+		$include_empty    = false;
+		$empty            = array();
 		// default value is full sync
 		if ( ! is_array( $module_configs ) ) {
 			$module_configs = array();
-			$include_empty = true;
-			foreach ( Jetpack_Sync_Modules::get_modules() as $module ) {
+			$include_empty  = true;
+			foreach ( Modules::get_modules() as $module ) {
 				$module_configs[ $module->name() ] = true;
 			}
 		}
 
 		// set default configuration, calculate totals, and save configuration if totals > 0
-		foreach ( Jetpack_Sync_Modules::get_modules() as $module ) {
+		foreach ( Modules::get_modules() as $module ) {
 			$module_name   = $module->name();
 			$module_config = isset( $module_configs[ $module_name ] ) ? $module_configs[ $module_name ] : false;
 
@@ -88,7 +90,7 @@ function start( $module_configs = null ) {
 					0,              // queued
 					false,          // current state
 				);
-			} else if ( $include_empty && $total_items === 0 ) {
+			} elseif ( $include_empty && $total_items === 0 ) {
 				$empty[ $module_name ] = true;
 			}
 		}
@@ -122,15 +124,15 @@ function continue_enqueuing( $configs = null, $enqueue_status = null ) {
 		}
 
 		// if full sync queue is full, don't enqueue more items
-		$max_queue_size_full_sync = Jetpack_Sync_Settings::get_setting( 'max_queue_size_full_sync' );
-		$full_sync_queue          = new Jetpack_Sync_Queue( 'full_sync' );
+		$max_queue_size_full_sync = Settings::get_setting( 'max_queue_size_full_sync' );
+		$full_sync_queue          = new Queue( 'full_sync' );
 
 		$available_queue_slots = $max_queue_size_full_sync - $full_sync_queue->size();
 
 		if ( $available_queue_slots <= 0 ) {
 			return;
 		} else {
-			$remaining_items_to_enqueue = min( Jetpack_Sync_Settings::get_setting( 'max_enqueue_full_sync' ), $available_queue_slots );
+			$remaining_items_to_enqueue = min( Settings::get_setting( 'max_enqueue_full_sync' ), $available_queue_slots );
 		}
 
 		if ( ! $configs ) {
@@ -141,7 +143,7 @@ function continue_enqueuing( $configs = null, $enqueue_status = null ) {
 			$enqueue_status = $this->get_enqueue_status();
 		}
 
-		foreach ( Jetpack_Sync_Modules::get_modules() as $module ) {
+		foreach ( Modules::get_modules() as $module ) {
 			$module_name = $module->name();
 
 			// skip module if not configured for this sync or module is done
@@ -202,13 +204,13 @@ function get_range( $type ) {
 			case 'posts':
 				$table     = $wpdb->posts;
 				$id        = 'ID';
-				$where_sql = Jetpack_Sync_Settings::get_blacklisted_post_types_sql();
+				$where_sql = Settings::get_blacklisted_post_types_sql();
 
 				break;
 			case 'comments':
 				$table     = $wpdb->comments;
 				$id        = 'comment_ID';
-				$where_sql = Jetpack_Sync_Settings::get_comments_filter_sql();
+				$where_sql = Settings::get_comments_filter_sql();
 				break;
 		}
 		$results = $wpdb->get_results( "SELECT MAX({$id}) as max, MIN({$id}) as min, COUNT({$id}) as count FROM {$table} WHERE {$where_sql}" );
@@ -247,7 +249,7 @@ function update_sent_progress_action( $actions ) {
 			$this->update_status_option( 'send_started', time() );
 		}
 
-		foreach ( Jetpack_Sync_Modules::get_modules() as $module ) {
+		foreach ( Modules::get_modules() as $module ) {
 			$module_actions     = $module->get_full_sync_actions();
 			$status_option_name = "{$module->name()}_sent";
 			$total_option_name  = "{$status_option_name}_total";
@@ -349,7 +351,7 @@ public function get_status() {
 
 		$enqueue_status = $this->get_enqueue_status();
 
-		foreach ( Jetpack_Sync_Modules::get_modules() as $module ) {
+		foreach ( Modules::get_modules() as $module ) {
 			$name = $module->name();
 
 			if ( ! isset( $enqueue_status[ $name ] ) ) {
@@ -381,60 +383,59 @@ public function get_status() {
 
 	public function clear_status() {
 		$prefix = self::STATUS_OPTION_PREFIX;
-		Jetpack_Options::delete_raw_option( "{$prefix}_started" );
-		Jetpack_Options::delete_raw_option( "{$prefix}_params" );
-		Jetpack_Options::delete_raw_option( "{$prefix}_queue_finished" );
-		Jetpack_Options::delete_raw_option( "{$prefix}_send_started" );
-		Jetpack_Options::delete_raw_option( "{$prefix}_finished" );
+		\Jetpack_Options::delete_raw_option( "{$prefix}_started" );
+		\Jetpack_Options::delete_raw_option( "{$prefix}_params" );
+		\Jetpack_Options::delete_raw_option( "{$prefix}_queue_finished" );
+		\Jetpack_Options::delete_raw_option( "{$prefix}_send_started" );
+		\Jetpack_Options::delete_raw_option( "{$prefix}_finished" );
 
 		$this->delete_enqueue_status();
 
-		foreach ( Jetpack_Sync_Modules::get_modules() as $module ) {
-			Jetpack_Options::delete_raw_option( "{$prefix}_{$module->name()}_sent" );
-			Jetpack_Options::delete_raw_option( "{$prefix}_{$module->name()}_sent_total" );
+		foreach ( Modules::get_modules() as $module ) {
+			\Jetpack_Options::delete_raw_option( "{$prefix}_{$module->name()}_sent" );
+			\Jetpack_Options::delete_raw_option( "{$prefix}_{$module->name()}_sent_total" );
 		}
 	}
 
 	public function reset_data() {
 		$this->clear_status();
 		$this->delete_config();
-		require_once dirname( __FILE__ ) . '/class.jetpack-sync-listener.php';
-		$listener = Jetpack_Sync_Listener::get_instance();
+		$listener = Listener::get_instance();
 		$listener->get_full_sync_queue()->reset();
 	}
 
 	private function get_status_option( $name, $default = null ) {
-		$value = Jetpack_Options::get_raw_option( self::STATUS_OPTION_PREFIX . "_$name", $default );
+		$value = \Jetpack_Options::get_raw_option( self::STATUS_OPTION_PREFIX . "_$name", $default );
 
 		return is_numeric( $value ) ? intval( $value ) : $value;
 	}
 
 	private function update_status_option( $name, $value, $autoload = false ) {
-		Jetpack_Options::update_raw_option( self::STATUS_OPTION_PREFIX . "_$name", $value, $autoload );
+		\Jetpack_Options::update_raw_option( self::STATUS_OPTION_PREFIX . "_$name", $value, $autoload );
 	}
 
 	private function set_enqueue_status( $new_status ) {
-		Jetpack_Options::update_raw_option( 'jetpack_sync_full_enqueue_status', $new_status );
+		\Jetpack_Options::update_raw_option( 'jetpack_sync_full_enqueue_status', $new_status );
 	}
 
 	private function delete_enqueue_status() {
-		return Jetpack_Options::delete_raw_option( 'jetpack_sync_full_enqueue_status' );
+		return \Jetpack_Options::delete_raw_option( 'jetpack_sync_full_enqueue_status' );
 	}
 
 	private function get_enqueue_status() {
-		return Jetpack_Options::get_raw_option( 'jetpack_sync_full_enqueue_status' );
+		return \Jetpack_Options::get_raw_option( 'jetpack_sync_full_enqueue_status' );
 	}
 
 	private function set_config( $config ) {
-		Jetpack_Options::update_raw_option( 'jetpack_sync_full_config', $config );
+		\Jetpack_Options::update_raw_option( 'jetpack_sync_full_config', $config );
 	}
 
 	private function delete_config() {
-		return Jetpack_Options::delete_raw_option( 'jetpack_sync_full_config' );
+		return \Jetpack_Options::delete_raw_option( 'jetpack_sync_full_config' );
 	}
 
 	private function get_config() {
-		return Jetpack_Options::get_raw_option( 'jetpack_sync_full_config' );
+		return \Jetpack_Options::get_raw_option( 'jetpack_sync_full_config' );
 	}
 
 	private function write_option( $name, $value ) {
diff --git a/sync/class.jetpack-sync-module-import.php b/packages/sync/src/Module_Import.php
similarity index 95%
rename from sync/class.jetpack-sync-module-import.php
rename to packages/sync/src/Module_Import.php
index 4b5dd83d36ed..ca97a26b57f4 100644
--- a/sync/class.jetpack-sync-module-import.php
+++ b/packages/sync/src/Module_Import.php
@@ -1,8 +1,8 @@
 <?php
 
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-settings.php';
+namespace Automattic\Jetpack\Sync;
 
-class Jetpack_Sync_Module_Import extends Jetpack_Sync_Module {
+class Module_Import extends Module {
 
 	/**
 	 * Tracks which actions have already been synced for the import
@@ -73,7 +73,7 @@ public function sync_import_action( $importer ) {
 		}
 
 		// Get $importer from known_importers.
-		$known_importers = Jetpack_Sync_Settings::get_setting( 'known_importers' );
+		$known_importers = Settings::get_setting( 'known_importers' );
 		if ( isset( $known_importers[ $importer ] ) ) {
 			$importer = $known_importers[ $importer ];
 		}
@@ -124,7 +124,7 @@ private function get_importer_name( $importer ) {
 	 */
 	private static function get_calling_importer_class() {
 		// If WP_Importer doesn't exist, neither will any importer that extends it.
-		if ( ! class_exists( 'WP_Importer', false ) ) {
+		if ( ! class_exists( '\\WP_Importer', false ) ) {
 			return 'unknown';
 		}
 
diff --git a/sync/class.jetpack-sync-module-menus.php b/packages/sync/src/Module_Menus.php
similarity index 97%
rename from sync/class.jetpack-sync-module-menus.php
rename to packages/sync/src/Module_Menus.php
index 86e2279c6b81..d64205192e44 100644
--- a/sync/class.jetpack-sync-module-menus.php
+++ b/packages/sync/src/Module_Menus.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_Menus extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_Menus extends Module {
 	private $nav_items_just_added = array();
 
 	function name() {
diff --git a/sync/class.jetpack-sync-module-meta.php b/packages/sync/src/Module_Meta.php
similarity index 96%
rename from sync/class.jetpack-sync-module-meta.php
rename to packages/sync/src/Module_Meta.php
index e3d4354495b7..afd018dd4f5c 100644
--- a/sync/class.jetpack-sync-module-meta.php
+++ b/packages/sync/src/Module_Meta.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_Meta extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_Meta extends Module {
 
 	public function name() {
 		return 'meta';
diff --git a/sync/class.jetpack-sync-module-network-options.php b/packages/sync/src/Module_Network_Options.php
similarity index 94%
rename from sync/class.jetpack-sync-module-network-options.php
rename to packages/sync/src/Module_Network_Options.php
index b2adefe8b88a..204c373b2f8e 100644
--- a/sync/class.jetpack-sync-module-network-options.php
+++ b/packages/sync/src/Module_Network_Options.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_Network_Options extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_Network_Options extends Module {
 	private $network_options_whitelist;
 
 	public function name() {
@@ -43,7 +45,7 @@ public function init_before_send() {
 	}
 
 	public function set_defaults() {
-		$this->network_options_whitelist = Jetpack_Sync_Defaults::$default_network_options_whitelist;
+		$this->network_options_whitelist = Defaults::$default_network_options_whitelist;
 	}
 
 	function enqueue_full_sync_actions( $config, $max_items_to_enqueue, $state ) {
diff --git a/sync/class.jetpack-sync-module-options.php b/packages/sync/src/Module_Options.php
similarity index 93%
rename from sync/class.jetpack-sync-module-options.php
rename to packages/sync/src/Module_Options.php
index 287e73b9fe53..d924e8cb4db0 100644
--- a/sync/class.jetpack-sync-module-options.php
+++ b/packages/sync/src/Module_Options.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_Options extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_Options extends Module {
 	private $options_whitelist, $options_contentless;
 
 	public function name() {
@@ -92,7 +94,7 @@ function get_all_options() {
 	}
 
 	function update_options_whitelist() {
-		$this->options_whitelist = Jetpack_Sync_Defaults::get_options_whitelist();
+		$this->options_whitelist = Defaults::get_options_whitelist();
 	}
 
 	function set_options_whitelist( $options ) {
@@ -104,7 +106,7 @@ function get_options_whitelist() {
 	}
 
 	function update_options_contentless() {
-		$this->options_contentless = Jetpack_Sync_Defaults::get_options_contentless();
+		$this->options_contentless = Defaults::get_options_contentless();
 	}
 
 	function get_options_contentless() {
@@ -157,9 +159,9 @@ function jetpack_sync_core_icon() {
 		// If there's a core icon, maybe update the option.  If not, fall back to Jetpack's.
 		if ( ! empty( $url ) && $url !== jetpack_site_icon_url() ) {
 			// This is the option that is synced with dotcom
-			Jetpack_Options::update_option( 'site_icon_url', $url );
+			\Jetpack_Options::update_option( 'site_icon_url', $url );
 		} elseif ( empty( $url ) ) {
-			Jetpack_Options::delete_option( 'site_icon_url' );
+			\Jetpack_Options::delete_option( 'site_icon_url' );
 		}
 	}
 
diff --git a/sync/class.jetpack-sync-module-plugins.php b/packages/sync/src/Module_Plugins.php
similarity index 98%
rename from sync/class.jetpack-sync-module-plugins.php
rename to packages/sync/src/Module_Plugins.php
index 876526abb6a5..e5bcbc8fbbc8 100644
--- a/sync/class.jetpack-sync-module-plugins.php
+++ b/packages/sync/src/Module_Plugins.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_Plugins extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_Plugins extends Module {
 
 	private $action_handler;
 	private $plugin_info = array();
@@ -65,7 +67,7 @@ public function on_upgrader_completion( $upgrader, $details ) {
 		switch ( $details['action'] ) {
 			case 'update':
 				$state  = array(
-					'is_autoupdate' => Jetpack_Constants::is_true( 'JETPACK_PLUGIN_AUTOUPDATE' ),
+					'is_autoupdate' => \Jetpack_Constants::is_true( 'JETPACK_PLUGIN_AUTOUPDATE' ),
 				);
 				$errors = $this->get_errors( $upgrader->skin );
 				if ( $errors ) {
diff --git a/sync/class.jetpack-sync-module-posts.php b/packages/sync/src/Module_Posts.php
similarity index 93%
rename from sync/class.jetpack-sync-module-posts.php
rename to packages/sync/src/Module_Posts.php
index 0384b64ffe1d..d4ae51304e4c 100644
--- a/sync/class.jetpack-sync-module-posts.php
+++ b/packages/sync/src/Module_Posts.php
@@ -1,8 +1,8 @@
 <?php
 
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-settings.php';
+namespace Automattic\Jetpack\Sync;
 
-class Jetpack_Sync_Module_Posts extends Jetpack_Sync_Module {
+class Module_Posts extends Module {
 
 	private $just_published  = array();
 	private $previous_status = array();
@@ -92,7 +92,7 @@ public function estimate_full_sync_actions( $config ) {
 	}
 
 	private function get_where_sql( $config ) {
-		$where_sql = Jetpack_Sync_Settings::get_blacklisted_post_types_sql();
+		$where_sql = Settings::get_blacklisted_post_types_sql();
 
 		// config is a list of post IDs to sync
 		if ( is_array( $config ) ) {
@@ -121,7 +121,7 @@ function expand_jetpack_sync_save_post( $args ) {
 	function filter_blacklisted_post_types( $args ) {
 		$post = $args[1];
 
-		if ( in_array( $post->post_type, Jetpack_Sync_Settings::get_setting( 'post_types_blacklist' ) ) ) {
+		if ( in_array( $post->post_type, Settings::get_setting( 'post_types_blacklist' ) ) ) {
 			return false;
 		}
 
@@ -139,13 +139,13 @@ function filter_meta( $args ) {
 
 	function is_whitelisted_post_meta( $meta_key ) {
 		// _wpas_skip_ is used by publicize
-		return in_array( $meta_key, Jetpack_Sync_Settings::get_setting( 'post_meta_whitelist' ) ) || wp_startswith( $meta_key, '_wpas_skip_' );
+		return in_array( $meta_key, Settings::get_setting( 'post_meta_whitelist' ) ) || wp_startswith( $meta_key, '_wpas_skip_' );
 	}
 
 	function is_post_type_allowed( $post_id ) {
 		$post = get_post( intval( $post_id ) );
 		if ( $post->post_type ) {
-			return ! in_array( $post->post_type, Jetpack_Sync_Settings::get_setting( 'post_types_blacklist' ) );
+			return ! in_array( $post->post_type, Settings::get_setting( 'post_types_blacklist' ) );
 		}
 		return false;
 	}
@@ -219,7 +219,7 @@ function filter_post_content_and_add_links( $post_object ) {
 		}
 
 		/** This filter is already documented in core. wp-includes/post-template.php */
-		if ( Jetpack_Sync_Settings::get_setting( 'render_filtered_content' ) && $post_type->public ) {
+		if ( Settings::get_setting( 'render_filtered_content' ) && $post_type->public ) {
 			global $shortcode_tags;
 			/**
 			 * Filter prevents some shortcodes from expanding.
@@ -318,7 +318,7 @@ public function wp_insert_post( $post_ID, $post = null, $update = null ) {
 			false;
 
 		$state = array(
-			'is_auto_save'                 => (bool) Jetpack_Constants::get_constant( 'DOING_AUTOSAVE' ),
+			'is_auto_save'                 => (bool) \Jetpack_Constants::get_constant( 'DOING_AUTOSAVE' ),
 			'previous_status'              => $previous_status,
 			'just_published'               => $just_published,
 			'is_gutenberg_meta_box_update' => $this->is_gutenberg_meta_box_update(),
@@ -423,9 +423,9 @@ public function expand_post_ids( $args ) {
 
 		return array(
 			$posts,
-			$this->get_metadata( $post_ids, 'post', Jetpack_Sync_Settings::get_setting( 'post_meta_whitelist' ) ),
+			$this->get_metadata( $post_ids, 'post', Settings::get_setting( 'post_meta_whitelist' ) ),
 			$this->get_term_relationships( $post_ids ),
-			$previous_interval_end
+			$previous_interval_end,
 		);
 	}
 }
diff --git a/sync/class.jetpack-sync-module-protect.php b/packages/sync/src/Module_Protect.php
similarity index 67%
rename from sync/class.jetpack-sync-module-protect.php
rename to packages/sync/src/Module_Protect.php
index a8dcd43e83ed..d6d0e73ae100 100644
--- a/sync/class.jetpack-sync-module-protect.php
+++ b/packages/sync/src/Module_Protect.php
@@ -1,9 +1,11 @@
 <?php
 
+namespace Automattic\Jetpack\Sync;
+
 /**
  * logs bruteprotect failed logins via sync
  */
-class Jetpack_Sync_Module_Protect extends Jetpack_Sync_Module {
+class Module_Protect extends Module {
 
 	function name() {
 		return 'protect';
@@ -15,8 +17,8 @@ function init_listeners( $callback ) {
 	}
 
 	function maybe_log_failed_login_attempt( $failed_attempt ) {
-		$protect = Jetpack_Protect_Module::instance();
-		if ( $protect->has_login_ability() && ! Jetpack_Constants::is_true( 'XMLRPC_REQUEST' ) ) {
+		$protect = \Jetpack_Protect_Module::instance();
+		if ( $protect->has_login_ability() && ! \Jetpack_Constants::is_true( 'XMLRPC_REQUEST' ) ) {
 			do_action( 'jetpack_valid_failed_login_attempt', $failed_attempt );
 		}
 	}
diff --git a/sync/class.jetpack-sync-module-stats.php b/packages/sync/src/Module_Stats.php
similarity index 82%
rename from sync/class.jetpack-sync-module-stats.php
rename to packages/sync/src/Module_Stats.php
index d23d3e008c81..47331fbc8d2f 100644
--- a/sync/class.jetpack-sync-module-stats.php
+++ b/packages/sync/src/Module_Stats.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_Stats extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_Stats extends Module {
 
 	function name() {
 		return 'stats';
@@ -23,6 +25,6 @@ public function init_before_send() {
 	}
 
 	public function add_stats() {
-		return array( Jetpack::get_stat_data( false, false ) );
+		return array( \Jetpack::get_stat_data( false, false ) );
 	}
 }
diff --git a/sync/class.jetpack-sync-module-terms.php b/packages/sync/src/Module_Terms.php
similarity index 88%
rename from sync/class.jetpack-sync-module-terms.php
rename to packages/sync/src/Module_Terms.php
index f09371c63fde..17bd63961116 100644
--- a/sync/class.jetpack-sync-module-terms.php
+++ b/packages/sync/src/Module_Terms.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_Terms extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_Terms extends Module {
 	private $taxonomy_whitelist;
 
 	function name() {
@@ -58,8 +60,8 @@ function get_full_sync_actions() {
 	}
 
 	function save_term_handler( $term_id, $tt_id, $taxonomy ) {
-		if ( class_exists( 'WP_Term' ) ) {
-			$term_object = WP_Term::get_instance( $term_id, $taxonomy );
+		if ( class_exists( '\\WP_Term' ) ) {
+			$term_object = \WP_Term::get_instance( $term_id, $taxonomy );
 		} else {
 			$term_object = get_term_by( 'id', $term_id, $taxonomy );
 		}
@@ -93,22 +95,22 @@ function set_taxonomy_whitelist( $taxonomies ) {
 	}
 
 	function set_defaults() {
-		$this->taxonomy_whitelist = Jetpack_Sync_Defaults::$default_taxonomy_whitelist;
+		$this->taxonomy_whitelist = Defaults::$default_taxonomy_whitelist;
 	}
 
 	public function expand_term_taxonomy_id( $args ) {
 		list( $term_taxonomy_ids,  $previous_end ) = $args;
 
-		return
-			array( 'terms' => get_terms(
+		return array(
+			'terms'        => get_terms(
 				array(
 					'hide_empty'       => false,
 					'term_taxonomy_id' => $term_taxonomy_ids,
 					'orderby'          => 'term_taxonomy_id',
-					'order'            => 'DESC'
+					'order'            => 'DESC',
 				)
 			),
-			'previous_end' => $previous_end
+			'previous_end' => $previous_end,
 		);
 	}
 }
diff --git a/sync/class.jetpack-sync-module-themes.php b/packages/sync/src/Module_Themes.php
similarity index 98%
rename from sync/class.jetpack-sync-module-themes.php
rename to packages/sync/src/Module_Themes.php
index e8b4185d0b7d..8cecfeca8178 100644
--- a/sync/class.jetpack-sync-module-themes.php
+++ b/packages/sync/src/Module_Themes.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_Themes extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_Themes extends Module {
 	function name() {
 		return 'themes';
 	}
@@ -293,7 +295,7 @@ public function check_upgrader( $upgrader, $details ) {
 
 		if ( 'install' === $details['action'] ) {
 			$theme = $upgrader->theme_info();
-			if ( ! $theme instanceof WP_Theme ) {
+			if ( ! $theme instanceof \WP_Theme ) {
 				return;
 			}
 			$theme_info = array(
@@ -324,7 +326,7 @@ public function check_upgrader( $upgrader, $details ) {
 			foreach ( $details['themes'] as $theme_slug ) {
 				$theme = wp_get_theme( $theme_slug );
 
-				if ( ! $theme instanceof WP_Theme ) {
+				if ( ! $theme instanceof \WP_Theme ) {
 					continue;
 				}
 
@@ -362,7 +364,7 @@ public function sync_theme_support( $new_name, $new_theme = null, $old_theme = n
 
 		/**
 		 * Fires when the client needs to sync theme support info
-		 * Only sends theme support attributes whitelisted in Jetpack_Sync_Defaults::$default_theme_support_whitelist
+		 * Only sends theme support attributes whitelisted in Defaults::$default_theme_support_whitelist
 		 *
 		 * @since 4.2.0
 		 *
@@ -578,7 +580,7 @@ private function get_theme_support_info( $theme = null ) {
 		if ( $theme === null ) {
 			$theme = wp_get_theme();
 
-			foreach ( Jetpack_Sync_Defaults::$default_theme_support_whitelist as $theme_feature ) {
+			foreach ( Defaults::$default_theme_support_whitelist as $theme_feature ) {
 				$has_support = current_theme_supports( $theme_feature );
 				if ( $has_support ) {
 					$theme_support[ $theme_feature ] = $_wp_theme_features[ $theme_feature ];
diff --git a/sync/class.jetpack-sync-module-updates.php b/packages/sync/src/Module_Updates.php
similarity index 97%
rename from sync/class.jetpack-sync-module-updates.php
rename to packages/sync/src/Module_Updates.php
index 4da4414fc073..6195ed63f600 100644
--- a/sync/class.jetpack-sync-module-updates.php
+++ b/packages/sync/src/Module_Updates.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_Updates extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_Updates extends Module {
 
 	const UPDATES_CHECKSUM_OPTION_NAME = 'jetpack_updates_sync_checksum';
 
@@ -102,7 +104,7 @@ public function update_core( $new_wp_version ) {
 		// Core was autoudpated
 		if (
 			'update-core.php' !== $pagenow &&
-			! Jetpack_Constants::is_true( 'REST_API_REQUEST' ) // wp.com rest api calls should never be marked as a core autoupdate
+			! \Jetpack_Constants::is_true( 'REST_API_REQUEST' ) // wp.com rest api calls should never be marked as a core autoupdate
 		) {
 			/**
 			 * Sync event that fires when core autoupdate was successful
diff --git a/sync/class.jetpack-sync-module-users.php b/packages/sync/src/Module_Users.php
similarity index 94%
rename from sync/class.jetpack-sync-module-users.php
rename to packages/sync/src/Module_Users.php
index f1cb47325c9b..96d2ffcac34a 100644
--- a/sync/class.jetpack-sync-module-users.php
+++ b/packages/sync/src/Module_Users.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_Users extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_Users extends Module {
 	const MAX_INITIAL_SYNC_USERS = 100;
 
 	protected $flags = array();
@@ -80,7 +82,7 @@ private function get_user( $user ) {
 		if ( is_numeric( $user ) ) {
 			$user = get_user_by( 'id', $user );
 		}
-		if ( $user instanceof WP_User ) {
+		if ( $user instanceof \WP_User ) {
 			return $user;
 		}
 		return null;
@@ -117,7 +119,7 @@ public function get_real_user_capabilities( $user ) {
 		if ( is_wp_error( $user ) ) {
 			return $user_capabilities;
 		}
-		foreach ( Jetpack_Sync_Defaults::get_capabilities_whitelist() as $capability ) {
+		foreach ( Defaults::get_capabilities_whitelist() as $capability ) {
 			if ( $user_has_capabilities = user_can( $user, $capability ) ) {
 				$user_capabilities[ $capability ] = true;
 			}
@@ -172,7 +174,7 @@ public function expand_logout_username( $args, $user_id ) {
 	 * @param String  $user_login the user login.
 	 * @param WP_User $user       the user object.
 	 */
-	 function wp_login_handler( $user_login, $user ) {
+	function wp_login_handler( $user_login, $user ) {
 		/**
 		 * Fires when a user is logged into a site.
 		 *
@@ -201,12 +203,12 @@ public function authenticate_handler( $user, $username, $password ) {
 		}
 
 		// We are only interested in successful authentication events.
-		if ( is_wp_error( $user ) || ! ( $user instanceof WP_User ) ) {
+		if ( is_wp_error( $user ) || ! ( $user instanceof \WP_User ) ) {
 			return $user;
 		}
 
 		jetpack_require_lib( 'class.jetpack-password-checker' );
-		$password_checker = new Jetpack_Password_Checker( $user->ID );
+		$password_checker = new \Jetpack_Password_Checker( $user->ID );
 
 		$test_results = $password_checker->test( $password, true );
 
@@ -218,8 +220,8 @@ public function authenticate_handler( $user, $username, $password ) {
 		$this->add_flags(
 			$user->ID,
 			array(
-				'warning'          => 'The password failed at least one strength test.',
-				'failures'         => $test_results['test_results']['failed'],
+				'warning'  => 'The password failed at least one strength test.',
+				'failures' => $test_results['test_results']['failed'],
 			)
 		);
 
@@ -246,7 +248,7 @@ function user_register_handler( $user_id, $old_user_data = null ) {
 			return;
 		}
 
-		if ( Jetpack_Constants::is_true( 'JETPACK_INVITE_ACCEPTED' ) ) {
+		if ( \Jetpack_Constants::is_true( 'JETPACK_INVITE_ACCEPTED' ) ) {
 			$this->add_flags( $user_id, array( 'invitation_accepted' => true ) );
 		}
 		/**
@@ -267,7 +269,7 @@ function add_user_to_blog_handler( $user_id, $old_user_data = null ) {
 			return;
 		}
 
-		if ( Jetpack_Constants::is_true( 'JETPACK_INVITE_ACCEPTED' ) ) {
+		if ( \Jetpack_Constants::is_true( 'JETPACK_INVITE_ACCEPTED' ) ) {
 			$this->add_flags( $user_id, array( 'invitation_accepted' => true ) );
 		}
 		/**
@@ -432,14 +434,17 @@ public function expand_users( $args ) {
 		list( $user_ids, $previous_end ) = $args;
 
 		return array(
-			'users' => array_map( array( $this, 'sanitize_user_and_expand' ), get_users(
-				array(
-					'include' => $user_ids,
-					'orderby' => 'ID',
-					'order' => 'DESC'
+			'users'        => array_map(
+				array( $this, 'sanitize_user_and_expand' ),
+				get_users(
+					array(
+						'include' => $user_ids,
+						'orderby' => 'ID',
+						'order'   => 'DESC',
+					)
 				)
-			) ),
-			'previous_end' => $previous_end
+			),
+			'previous_end' => $previous_end,
 		);
 	}
 
diff --git a/sync/class.jetpack-sync-module-wp-super-cache.php b/packages/sync/src/Module_WP_Super_Cache.php
similarity index 93%
rename from sync/class.jetpack-sync-module-wp-super-cache.php
rename to packages/sync/src/Module_WP_Super_Cache.php
index 04d6c5dd4240..c2e69454082c 100644
--- a/sync/class.jetpack-sync-module-wp-super-cache.php
+++ b/packages/sync/src/Module_WP_Super_Cache.php
@@ -1,6 +1,8 @@
 <?php
 
-class Jetpack_Sync_Module_WP_Super_Cache extends Jetpack_Sync_Module {
+namespace Automattic\Jetpack\Sync;
+
+class Module_WP_Super_Cache extends Module {
 
 	public function __construct() {
 		add_filter( 'jetpack_sync_constants_whitelist', array( $this, 'add_wp_super_cache_constants_whitelist' ), 10 );
@@ -16,7 +18,7 @@ public function __construct() {
 	);
 
 	static $wp_super_cache_callables = array(
-		'wp_super_cache_globals' => array( 'Jetpack_Sync_Module_WP_Super_Cache', 'get_wp_super_cache_globals' ),
+		'wp_super_cache_globals' => array( 'Module_WP_Super_Cache', 'get_wp_super_cache_globals' ),
 	);
 
 	public function name() {
diff --git a/sync/class.jetpack-sync-module-woocommerce.php b/packages/sync/src/Module_WooCommerce.php
similarity index 98%
rename from sync/class.jetpack-sync-module-woocommerce.php
rename to packages/sync/src/Module_WooCommerce.php
index 962258a2ffa5..68cb182242a9 100644
--- a/sync/class.jetpack-sync-module-woocommerce.php
+++ b/packages/sync/src/Module_WooCommerce.php
@@ -1,8 +1,8 @@
 <?php
 
-require_once JETPACK__PLUGIN_DIR . '/sync/class.jetpack-sync-module.php';
+namespace Automattic\Jetpack\Sync;
 
-class Jetpack_Sync_Module_WooCommerce extends Jetpack_Sync_Module {
+class Module_WooCommerce extends Module {
 
 	private $order_item_meta_whitelist = array(
 		// https://github.com/woocommerce/woocommerce/blob/master/includes/data-stores/class-wc-order-item-product-store.php#L20
diff --git a/packages/sync/src/Modules.php b/packages/sync/src/Modules.php
new file mode 100644
index 000000000000..bf37f169c9df
--- /dev/null
+++ b/packages/sync/src/Modules.php
@@ -0,0 +1,86 @@
+<?php
+
+namespace Automattic\Jetpack\Sync;
+
+/**
+ * simple wrapper that allows enumerating cached static instances
+ * of sync modules
+ */
+
+class Modules {
+
+	private static $default_sync_modules = array(
+		__NAMESPACE__ . '\\Module_Constants',
+		__NAMESPACE__ . '\\Module_Callables',
+		__NAMESPACE__ . '\\Module_Options',
+		__NAMESPACE__ . '\\Module_Network_Options',
+		__NAMESPACE__ . '\\Module_Terms',
+		__NAMESPACE__ . '\\Module_Themes',
+		__NAMESPACE__ . '\\Module_Menus',
+		__NAMESPACE__ . '\\Module_Users',
+		__NAMESPACE__ . '\\Module_Posts',
+		__NAMESPACE__ . '\\Module_Import',
+		__NAMESPACE__ . '\\Module_Protect',
+		__NAMESPACE__ . '\\Module_Comments',
+		__NAMESPACE__ . '\\Module_Updates',
+		__NAMESPACE__ . '\\Module_Attachments',
+		__NAMESPACE__ . '\\Module_Meta',
+		__NAMESPACE__ . '\\Module_Plugins',
+		__NAMESPACE__ . '\\Module_Full_Sync',
+		__NAMESPACE__ . '\\Module_Stats',
+	);
+
+	private static $initialized_modules = null;
+
+	public static function get_modules() {
+		if ( null === self::$initialized_modules ) {
+			self::$initialized_modules = self::initialize_modules();
+		}
+
+		return self::$initialized_modules;
+	}
+
+	public static function set_defaults() {
+		foreach ( self::get_modules() as $module ) {
+			$module->set_defaults();
+		}
+	}
+
+	public static function get_module( $module_name ) {
+		foreach ( self::get_modules() as $module ) {
+			if ( $module->name() === $module_name ) {
+				return $module;
+			}
+		}
+
+		return false;
+	}
+
+	static function initialize_modules() {
+		/**
+		 * Filters the list of class names of sync modules.
+		 * If you add to this list, make sure any classes implement the
+		 * Module interface.
+		 *
+		 * @since 4.2.0
+		 */
+		$modules = apply_filters( 'jetpack_sync_modules', self::$default_sync_modules );
+
+		$modules = array_map( array( __NAMESPACE__ . '\\Modules', 'load_module' ), $modules );
+
+		return array_map( array( __NAMESPACE__ . '\\Modules', 'set_module_defaults' ), $modules );
+	}
+
+	static function load_module( $module_name ) {
+		return new $module_name();
+	}
+
+	static function set_module_defaults( $module ) {
+		$module->set_defaults();
+		if ( method_exists( $module, 'set_late_default' ) ) {
+			add_action( 'init', array( $module, 'set_late_default' ), 90 );
+		}
+		return $module;
+	}
+
+}
diff --git a/sync/class.jetpack-sync-queue.php b/packages/sync/src/Queue.php
similarity index 82%
rename from sync/class.jetpack-sync-queue.php
rename to packages/sync/src/Queue.php
index ae40a597f459..9551399b0ed2 100644
--- a/sync/class.jetpack-sync-queue.php
+++ b/packages/sync/src/Queue.php
@@ -1,29 +1,6 @@
 <?php
 
-/**
- * A buffer of items from the queue that can be checked out
- */
-class Jetpack_Sync_Queue_Buffer {
-	public $id;
-	public $items_with_ids;
-
-	public function __construct( $id, $items_with_ids ) {
-		$this->id             = $id;
-		$this->items_with_ids = $items_with_ids;
-	}
-
-	public function get_items() {
-		return array_combine( $this->get_item_ids(), $this->get_item_values() );
-	}
-
-	public function get_item_values() {
-		return Jetpack_Sync_Utils::get_item_values( $this->items_with_ids );
-	}
-
-	public function get_item_ids() {
-		return Jetpack_Sync_Utils::get_item_ids( $this->items_with_ids );
-	}
-}
+namespace Automattic\Jetpack\Sync;
 
 /**
  * A persistent queue that can be flushed in increments of N items,
@@ -31,7 +8,7 @@ public function get_item_ids() {
  * closed. This uses raw SQL for two reasons: speed, and not triggering
  * tons of added_option callbacks.
  */
-class Jetpack_Sync_Queue {
+class Queue {
 	public $id;
 	private $row_iterator;
 
@@ -77,7 +54,7 @@ function add_all( $items ) {
 		$rows_added = $wpdb->query( $query . join( ',', $rows ) );
 
 		if ( count( $items ) === $rows_added ) {
-			return new WP_Error( 'row_count_mismatch', "The number of rows inserted didn't match the size of the input array" );
+			return new \WP_Error( 'row_count_mismatch', "The number of rows inserted didn't match the size of the input array" );
 		}
 	}
 
@@ -85,7 +62,7 @@ function add_all( $items ) {
 	function peek( $count = 1 ) {
 		$items = $this->fetch_items( $count );
 		if ( $items ) {
-			return Jetpack_Sync_Utils::get_item_values( $items );
+			return Utils::get_item_values( $items );
 		}
 
 		return array();
@@ -157,7 +134,7 @@ function has_any_items() {
 
 	function checkout( $buffer_size ) {
 		if ( $this->get_checkout_id() ) {
-			return new WP_Error( 'unclosed_buffer', 'There is an unclosed buffer' );
+			return new \WP_Error( 'unclosed_buffer', 'There is an unclosed buffer' );
 		}
 
 		$buffer_id = uniqid();
@@ -174,7 +151,7 @@ function checkout( $buffer_size ) {
 			return false;
 		}
 
-		$buffer = new Jetpack_Sync_Queue_Buffer( $buffer_id, array_slice( $items, 0, $buffer_size ) );
+		$buffer = new Queue_Buffer( $buffer_id, array_slice( $items, 0, $buffer_size ) );
 
 		return $buffer;
 	}
@@ -186,7 +163,7 @@ function checkout( $buffer_size ) {
 	// exceeds the memory limit, but in that case it will send that item by itself.
 	function checkout_with_memory_limit( $max_memory, $max_buffer_size = 500 ) {
 		if ( $this->get_checkout_id() ) {
-			return new WP_Error( 'unclosed_buffer', 'There is an unclosed buffer' );
+			return new \WP_Error( 'unclosed_buffer', 'There is an unclosed buffer' );
 		}
 
 		$buffer_id = uniqid();
@@ -246,7 +223,7 @@ function checkout_with_memory_limit( $max_memory, $max_buffer_size = 500 ) {
 			return false;
 		}
 
-		$buffer = new Jetpack_Sync_Queue_Buffer( $buffer_id, $items );
+		$buffer = new Queue_Buffer( $buffer_id, $items );
 
 		return $buffer;
 	}
@@ -289,7 +266,7 @@ function close( $buffer, $ids_to_remove = null ) {
 	}
 
 	function flush_all() {
-		$items = Jetpack_Sync_Utils::get_item_values( $this->fetch_items() );
+		$items = Utils::get_item_values( $this->fetch_items() );
 		$this->reset();
 
 		return $items;
@@ -316,11 +293,11 @@ function lock( $timeout = 30 ) {
 		}
 
 		if ( $tries === 30 ) {
-			return new WP_Error( 'lock_timeout', 'Timeout waiting for sync queue to empty' );
+			return new \WP_Error( 'lock_timeout', 'Timeout waiting for sync queue to empty' );
 		}
 
 		if ( $this->get_checkout_id() ) {
-			return new WP_Error( 'unclosed_buffer', 'There is an unclosed buffer' );
+			return new \WP_Error( 'unclosed_buffer', 'There is an unclosed buffer' );
 		}
 
 		// hopefully this means we can acquire a checkout?
@@ -370,7 +347,7 @@ private function get_checkout_id() {
 	private function set_checkout_id( $checkout_id ) {
 		global $wpdb;
 
-		$expires     = time() + Jetpack_Sync_Defaults::$default_sync_queue_lock_timeout;
+		$expires     = time() + Defaults::$default_sync_queue_lock_timeout;
 		$updated_num = $wpdb->query(
 			$wpdb->prepare(
 				"UPDATE $wpdb->options SET option_value = %s WHERE option_name = %s",
@@ -440,39 +417,20 @@ private function fetch_items( $limit = null ) {
 	}
 
 	private function validate_checkout( $buffer ) {
-		if ( ! $buffer instanceof Jetpack_Sync_Queue_Buffer ) {
-			return new WP_Error( 'not_a_buffer', 'You must checkin an instance of Jetpack_Sync_Queue_Buffer' );
+		if ( ! $buffer instanceof Queue_Buffer ) {
+			return new \WP_Error( 'not_a_buffer', 'You must checkin an instance of Queue_Buffer' );
 		}
 
 		$checkout_id = $this->get_checkout_id();
 
 		if ( ! $checkout_id ) {
-			return new WP_Error( 'buffer_not_checked_out', 'There are no checked out buffers' );
+			return new \WP_Error( 'buffer_not_checked_out', 'There are no checked out buffers' );
 		}
 
 		if ( $checkout_id != $buffer->id ) {
-			return new WP_Error( 'buffer_mismatch', 'The buffer you checked in was not checked out' );
+			return new \WP_Error( 'buffer_mismatch', 'The buffer you checked in was not checked out' );
 		}
 
 		return true;
 	}
 }
-
-class Jetpack_Sync_Utils {
-
-	static function get_item_values( $items ) {
-		return array_map( array( __CLASS__, 'get_item_value' ), $items );
-	}
-
-	static function get_item_ids( $items ) {
-		return array_map( array( __CLASS__, 'get_item_id' ), $items );
-	}
-
-	private static function get_item_value( $item ) {
-		return $item->value;
-	}
-
-	private static function get_item_id( $item ) {
-		return $item->id;
-	}
-}
diff --git a/packages/sync/src/Queue_Buffer.php b/packages/sync/src/Queue_Buffer.php
new file mode 100644
index 000000000000..c37a2dc76e03
--- /dev/null
+++ b/packages/sync/src/Queue_Buffer.php
@@ -0,0 +1,28 @@
+<?php
+
+namespace Automattic\Jetpack\Sync;
+
+/**
+ * A buffer of items from the queue that can be checked out
+ */
+class Queue_Buffer {
+	public $id;
+	public $items_with_ids;
+
+	public function __construct( $id, $items_with_ids ) {
+		$this->id             = $id;
+		$this->items_with_ids = $items_with_ids;
+	}
+
+	public function get_items() {
+		return array_combine( $this->get_item_ids(), $this->get_item_values() );
+	}
+
+	public function get_item_values() {
+		return Utils::get_item_values( $this->items_with_ids );
+	}
+
+	public function get_item_ids() {
+		return Utils::get_item_ids( $this->items_with_ids );
+	}
+}
diff --git a/sync/interface.jetpack-sync-replicastore.php b/packages/sync/src/Replicastore.php
similarity index 98%
rename from sync/interface.jetpack-sync-replicastore.php
rename to packages/sync/src/Replicastore.php
index c22f4e519628..29ff62a49466 100644
--- a/sync/interface.jetpack-sync-replicastore.php
+++ b/packages/sync/src/Replicastore.php
@@ -6,12 +6,14 @@
  * To run tests: phpunit --testsuite sync --filter New_Sync
  */
 
+namespace Automattic\Jetpack\Sync;
+
 /**
  * A high-level interface for objects that store synced WordPress data
  * Useful for ensuring that different storage mechanisms implement the
  * required semantics for storing all the data that we sync
  */
-interface iJetpack_Sync_Replicastore {
+interface Replicastore {
 	// remove all data
 	public function reset();
 
diff --git a/sync/class.jetpack-sync-sender.php b/packages/sync/src/Sender.php
similarity index 84%
rename from sync/class.jetpack-sync-sender.php
rename to packages/sync/src/Sender.php
index 21f914819310..010d5d1ab2b3 100644
--- a/sync/class.jetpack-sync-sender.php
+++ b/packages/sync/src/Sender.php
@@ -1,17 +1,11 @@
 <?php
 
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-queue.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-defaults.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-json-deflate-array-codec.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-simple-codec.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-modules.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-settings.php';
+namespace Automattic\Jetpack\Sync;
 
 /**
  * This class grabs pending actions from the queue and sends them
  */
-class Jetpack_Sync_Sender {
-
+class Sender {
 	const NEXT_SYNC_TIME_OPTION_NAME = 'jetpack_next_sync_time';
 	const WPCOM_ERROR_SYNC_DELAY     = 60;
 	const QUEUE_LOCKED_SYNC_DELAY    = 10;
@@ -48,15 +42,15 @@ protected function __construct() {
 	private function init() {
 		add_action( 'jetpack_sync_before_send_queue_sync', array( $this, 'maybe_set_user_from_token' ), 1 );
 		add_action( 'jetpack_sync_before_send_queue_sync', array( $this, 'maybe_clear_user_from_token' ), 20 );
-		foreach ( Jetpack_Sync_Modules::get_modules() as $module ) {
+		foreach ( Modules::get_modules() as $module ) {
 			$module->init_before_send();
 		}
 	}
 
 	public function maybe_set_user_from_token() {
-		$jetpack       = Jetpack::init();
+		$jetpack       = \Jetpack::init();
 		$verified_user = $jetpack->verify_xml_rpc_signature();
-		if ( Jetpack_Constants::is_true( 'XMLRPC_REQUEST' ) &&
+		if ( \Jetpack_Constants::is_true( 'XMLRPC_REQUEST' ) &&
 			! is_wp_error( $verified_user )
 			&& $verified_user
 		) {
@@ -81,7 +75,7 @@ public function set_next_sync_time( $time, $queue_name ) {
 	}
 
 	public function do_full_sync() {
-		if ( ! Jetpack_Sync_Modules::get_module( 'full-sync' ) ) {
+		if ( ! Modules::get_module( 'full-sync' ) ) {
 			return;
 		}
 		$this->continue_full_sync_enqueue();
@@ -97,7 +91,7 @@ private function continue_full_sync_enqueue() {
 			return false;
 		}
 
-		Jetpack_Sync_Modules::get_module( 'full-sync' )->continue_enqueuing();
+		Modules::get_module( 'full-sync' )->continue_enqueuing();
 
 		$this->set_next_sync_time( time() + $this->get_enqueue_wait_time(), 'full-sync-enqueue' );
 	}
@@ -109,21 +103,21 @@ public function do_sync() {
 	public function do_sync_and_set_delays( $queue ) {
 		// don't sync if importing
 		if ( defined( 'WP_IMPORTING' ) && WP_IMPORTING ) {
-			return new WP_Error( 'is_importing' );
+			return new \WP_Error( 'is_importing' );
 		}
 
 		// don't sync if we are throttled
 		if ( $this->get_next_sync_time( $queue->id ) > microtime( true ) ) {
-			return new WP_Error( 'sync_throttled' );
+			return new \WP_Error( 'sync_throttled' );
 		}
 
 		$start_time = microtime( true );
 
-		Jetpack_Sync_Settings::set_is_syncing( true );
+		Settings::set_is_syncing( true );
 
 		$sync_result = $this->do_sync_for_queue( $queue );
 
-		Jetpack_Sync_Settings::set_is_syncing( false );
+		Settings::set_is_syncing( false );
 
 		$exceeded_sync_wait_threshold = ( microtime( true ) - $start_time ) > (float) $this->get_sync_wait_threshold();
 
@@ -197,7 +191,7 @@ private function fastcgi_finish_request() {
 	public function do_sync_for_queue( $queue ) {
 		do_action( 'jetpack_sync_before_send_queue_' . $queue->id );
 		if ( $queue->size() === 0 ) {
-			return new WP_Error( 'empty_queue_' . $queue->id );
+			return new \WP_Error( 'empty_queue_' . $queue->id );
 		}
 		// now that we're sure we are about to sync, try to
 		// ignore user abort so we can avoid getting into a
@@ -207,7 +201,7 @@ public function do_sync_for_queue( $queue ) {
 		}
 
 		/* Don't make the request block till we finish, if possible. */
-		if ( Jetpack_Constants::is_true( 'REST_REQUEST' ) || Jetpack_Constants::is_true('XMLRPC_REQUEST' ) ) {
+		if ( \Jetpack_Constants::is_true( 'REST_REQUEST' ) || \Jetpack_Constants::is_true( 'XMLRPC_REQUEST' ) ) {
 			$this->fastcgi_finish_request();
 		}
 
@@ -217,7 +211,7 @@ public function do_sync_for_queue( $queue ) {
 
 		if ( ! $buffer ) {
 			// buffer has no items
-			return new WP_Error( 'empty_buffer' );
+			return new \WP_Error( 'empty_buffer' );
 		}
 
 		if ( is_wp_error( $buffer ) ) {
@@ -240,9 +234,9 @@ public function do_sync_for_queue( $queue ) {
 			 * @param double $time The current time
 			 * @param string $queue The queue used to send ('sync' or 'full_sync')
 			 */
-			Jetpack_Sync_Settings::set_is_sending( true );
+			Settings::set_is_sending( true );
 			$processed_item_ids = apply_filters( 'jetpack_sync_send_data', $items_to_send, $this->codec->name(), microtime( true ), $queue->id, $checkout_duration, $preprocess_duration );
-			Jetpack_Sync_Settings::set_is_sending( false );
+			Settings::set_is_sending( false );
 		} else {
 			$processed_item_ids = $skipped_items_ids;
 			$skipped_items_ids  = array();
@@ -255,11 +249,11 @@ public function do_sync_for_queue( $queue ) {
 				$queue->force_checkin();
 			}
 			if ( is_wp_error( $processed_item_ids ) ) {
-				return new WP_Error( 'wpcom_error', $processed_item_ids->get_error_code() );
+				return new \WP_Error( 'wpcom_error', $processed_item_ids->get_error_code() );
 			}
 			// returning a WP_Error('wpcom_error') is a sign to the caller that we should wait a while
 			// before syncing again
-			return new WP_Error( 'wpcom_error', 'jetpack_sync_send_data_false' );
+			return new \WP_Error( 'wpcom_error', 'jetpack_sync_send_data_false' );
 		} else {
 			// detect if the last item ID was an error
 			$had_wp_error = is_wp_error( end( $processed_item_ids ) );
@@ -284,7 +278,7 @@ public function do_sync_for_queue( $queue ) {
 			// returning a WP_Error is a sign to the caller that we should wait a while
 			// before syncing again
 			if ( $had_wp_error ) {
-				return new WP_Error( 'wpcom_error', $wp_error->get_error_code() );
+				return new \WP_Error( 'wpcom_error', $wp_error->get_error_code() );
 			}
 		}
 		return true;
@@ -303,15 +297,14 @@ function get_codec() {
 	}
 	function set_codec() {
 		if ( function_exists( 'gzinflate' ) ) {
-			$this->codec = new Jetpack_Sync_JSON_Deflate_Array_Codec();
+			$this->codec = new JSON_Deflate_Array_Codec();
 		} else {
-			$this->codec = new Jetpack_Sync_Simple_Codec();
+			$this->codec = new Simple_Codec();
 		}
 	}
 
 	function send_checksum() {
-		require_once 'class.jetpack-sync-wp-replicastore.php';
-		$store = new Jetpack_Sync_WP_Replicastore();
+		$store = new WP_Replicastore();
 		do_action( 'jetpack_sync_checksum', $store->checksum_all() );
 	}
 
@@ -371,27 +364,27 @@ function set_max_dequeue_time( $seconds ) {
 
 
 	function set_defaults() {
-		$this->sync_queue      = new Jetpack_Sync_Queue( 'sync' );
-		$this->full_sync_queue = new Jetpack_Sync_Queue( 'full_sync' );
+		$this->sync_queue      = new Queue( 'sync' );
+		$this->full_sync_queue = new Queue( 'full_sync' );
 		$this->set_codec();
 
 		// saved settings
-		Jetpack_Sync_Settings::set_importing( null );
-		$settings = Jetpack_Sync_Settings::get_settings();
+		Settings::set_importing( null );
+		$settings = Settings::get_settings();
 		$this->set_dequeue_max_bytes( $settings['dequeue_max_bytes'] );
 		$this->set_upload_max_bytes( $settings['upload_max_bytes'] );
 		$this->set_upload_max_rows( $settings['upload_max_rows'] );
 		$this->set_sync_wait_time( $settings['sync_wait_time'] );
 		$this->set_enqueue_wait_time( $settings['enqueue_wait_time'] );
 		$this->set_sync_wait_threshold( $settings['sync_wait_threshold'] );
-		$this->set_max_dequeue_time( Jetpack_Sync_Defaults::get_max_sync_execution_time() );
+		$this->set_max_dequeue_time( Defaults::get_max_sync_execution_time() );
 	}
 
 	function reset_data() {
 		$this->reset_sync_queue();
 		$this->reset_full_sync_queue();
 
-		foreach ( Jetpack_Sync_Modules::get_modules() as $module ) {
+		foreach ( Modules::get_modules() as $module ) {
 			$module->reset_data();
 		}
 
@@ -399,7 +392,7 @@ function reset_data() {
 			delete_option( self::NEXT_SYNC_TIME_OPTION_NAME . '_' . $queue_name );
 		}
 
-		Jetpack_Sync_Settings::reset_data();
+		Settings::reset_data();
 	}
 
 	function uninstall() {
diff --git a/sync/class.jetpack-sync-server.php b/packages/sync/src/Server.php
similarity index 88%
rename from sync/class.jetpack-sync-server.php
rename to packages/sync/src/Server.php
index dbd9172aa1d0..e0da4a42bc35 100644
--- a/sync/class.jetpack-sync-server.php
+++ b/packages/sync/src/Server.php
@@ -1,12 +1,12 @@
 <?php
 
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-json-deflate-array-codec.php';
+namespace Automattic\Jetpack\Sync;
 
 /**
  * Simple version of a Jetpack Sync Server - just receives arrays of events and
  * issues them locally with the 'jetpack_sync_remote_action' action.
  */
-class Jetpack_Sync_Server {
+class Server {
 	private $codec;
 	const MAX_TIME_PER_REQUEST_IN_SECONDS = 15;
 	const BLOG_LOCK_TRANSIENT_PREFIX      = 'jp_sync_req_lock_';
@@ -14,10 +14,10 @@ class Jetpack_Sync_Server {
 
 	// this is necessary because you can't use "new" when you declare instance properties >:(
 	function __construct() {
-		$this->codec = new Jetpack_Sync_JSON_Deflate_Array_Codec();
+		$this->codec = new JSON_Deflate_Array_Codec();
 	}
 
-	function set_codec( iJetpack_Sync_Codec $codec ) {
+	function set_codec( Codec $codec ) {
 		$this->codec = $codec;
 	}
 
@@ -43,7 +43,7 @@ function remove_request_lock( $blog_id ) {
 	function receive( $data, $token = null, $sent_timestamp = null, $queue_id = null ) {
 		$start_time = microtime( true );
 		if ( ! is_array( $data ) ) {
-			return new WP_Error( 'action_decoder_error', 'Events must be an array' );
+			return new \WP_Error( 'action_decoder_error', 'Events must be an array' );
 		}
 
 		if ( $token && ! $this->attempt_request_lock( $token->blog_id ) ) {
@@ -56,7 +56,7 @@ function receive( $data, $token = null, $sent_timestamp = null, $queue_id = null
 			 */
 			do_action( 'jetpack_sync_multi_request_fail', $token );
 
-			return new WP_Error( 'concurrent_request_error', 'There is another request running for the same blog ID' );
+			return new \WP_Error( 'concurrent_request_error', 'There is another request running for the same blog ID' );
 		}
 
 		$events           = wp_unslash( array_map( array( $this->codec, 'decode' ), $data ) );
diff --git a/sync/class.jetpack-sync-settings.php b/packages/sync/src/Settings.php
similarity index 89%
rename from sync/class.jetpack-sync-settings.php
rename to packages/sync/src/Settings.php
index e77588a87183..ab695008fc71 100644
--- a/sync/class.jetpack-sync-settings.php
+++ b/packages/sync/src/Settings.php
@@ -1,8 +1,8 @@
 <?php
 
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-defaults.php';
+namespace Automattic\Jetpack\Sync;
 
-class Jetpack_Sync_Settings {
+class Settings {
 	const SETTINGS_OPTION_PREFIX = 'jetpack_sync_settings_';
 
 	static $valid_settings = array(
@@ -60,7 +60,7 @@ static function get_setting( $setting ) {
 				$value = get_site_option( self::SETTINGS_OPTION_PREFIX . $setting );
 			} else {
 				// On single sites just return the default setting
-				$value = Jetpack_Sync_Defaults::get_default_setting( $setting );
+				$value = Defaults::get_default_setting( $setting );
 				self::$settings_cache[ $setting ] = $value;
 				return $value;
 			}
@@ -69,7 +69,7 @@ static function get_setting( $setting ) {
 		}
 
 		if ( false === $value ) { // no default value is set.
-			$value = Jetpack_Sync_Defaults::get_default_setting( $setting );
+			$value = Defaults::get_default_setting( $setting );
 			if ( self::is_network_setting( $setting ) ) {
 				update_site_option( self::SETTINGS_OPTION_PREFIX . $setting, $value );
 			} else {
@@ -84,16 +84,16 @@ static function get_setting( $setting ) {
 		$default_array_value = null;
 		switch ( $setting ) {
 			case 'post_types_blacklist':
-				$default_array_value = Jetpack_Sync_Defaults::$blacklisted_post_types;
+				$default_array_value = Defaults::$blacklisted_post_types;
 				break;
 			case 'post_meta_whitelist':
-				$default_array_value = Jetpack_Sync_Defaults::get_post_meta_whitelist();
+				$default_array_value = Defaults::get_post_meta_whitelist();
 				break;
 			case 'comment_meta_whitelist':
-				$default_array_value = Jetpack_Sync_Defaults::get_comment_meta_whitelist();
+				$default_array_value = Defaults::get_comment_meta_whitelist();
 				break;
 			case 'known_importers':
-				$default_array_value = Jetpack_Sync_Defaults::get_known_importers();
+				$default_array_value = Defaults::get_known_importers();
 				break;
 		}
 
@@ -126,8 +126,7 @@ static function update_settings( $new_settings ) {
 
 			// if we set the disabled option to true, clear the queues
 			if ( ( 'disable' === $setting || 'network_disable' === $setting ) && ! ! $value ) {
-				require_once dirname( __FILE__ ) . '/class.jetpack-sync-listener.php';
-				$listener = Jetpack_Sync_Listener::get_instance();
+				$listener = Listener::get_instance();
 				$listener->get_sync_queue()->reset();
 				$listener->get_full_sync_queue()->reset();
 			}
diff --git a/sync/class.jetpack-sync-simple-codec.php b/packages/sync/src/Simple_Codec.php
similarity index 61%
rename from sync/class.jetpack-sync-simple-codec.php
rename to packages/sync/src/Simple_Codec.php
index 7bd9aaac3c25..fa49052702f1 100644
--- a/sync/class.jetpack-sync-simple-codec.php
+++ b/packages/sync/src/Simple_Codec.php
@@ -1,12 +1,12 @@
 <?php
 
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-json-deflate-array-codec.php';
+namespace Automattic\Jetpack\Sync;
 
 /**
- * An implementation of iJetpack_Sync_Codec that uses gzip's DEFLATE
+ * An implementation of Codec that uses gzip's DEFLATE
  * algorithm to compress objects serialized using json_encode
  */
-class Jetpack_Sync_Simple_Codec extends Jetpack_Sync_JSON_Deflate_Array_Codec {
+class Simple_Codec extends JSON_Deflate_Array_Codec {
 	const CODEC_NAME = 'simple';
 
 	public function name() {
diff --git a/sync/class.jetpack-sync-users.php b/packages/sync/src/Users.php
similarity index 71%
rename from sync/class.jetpack-sync-users.php
rename to packages/sync/src/Users.php
index de032e2d2ff3..88728cd3234b 100644
--- a/sync/class.jetpack-sync-users.php
+++ b/packages/sync/src/Users.php
@@ -1,15 +1,17 @@
 <?php
 
+namespace Automattic\Jetpack\Sync;
+
 /**
- * Class Jetpack_Sync_Users
+ * Class Users
  *
  * Responsible for syncing user data changes.
  */
-class Jetpack_Sync_Users {
+class Users {
 	static $user_roles = array();
 
 	static function init() {
-		if ( Jetpack::is_active() ) {
+		if ( \Jetpack::is_active() ) {
 			// Kick off synchronization of user role when it changes
 			add_action( 'set_user_role', array( __CLASS__, 'user_role_change' ) );
 		}
@@ -19,7 +21,7 @@ static function init() {
 	 * Synchronize connected user role changes
 	 */
 	static function user_role_change( $user_id ) {
-		if ( Jetpack::is_user_connected( $user_id ) ) {
+		if ( \Jetpack::is_user_connected( $user_id ) ) {
 			self::update_role_on_com( $user_id );
 			// try to choose a new master if we're demoting the current one
 			self::maybe_demote_master_user( $user_id );
@@ -33,7 +35,7 @@ static function get_role( $user_id ) {
 
 		$current_user_id = get_current_user_id();
 		wp_set_current_user( $user_id );
-		$role = Jetpack::translate_current_user_to_role();
+		$role = \Jetpack::translate_current_user_to_role();
 		wp_set_current_user( $current_user_id );
 		$user_roles[ $user_id ] = $role;
 
@@ -41,19 +43,19 @@ static function get_role( $user_id ) {
 	}
 
 	static function get_signed_role( $user_id ) {
-		return Jetpack::sign_role( self::get_role( $user_id ), $user_id );
+		return \Jetpack::sign_role( self::get_role( $user_id ), $user_id );
 	}
 
 	static function update_role_on_com( $user_id ) {
 		$signed_role = self::get_signed_role( $user_id );
-		Jetpack::xmlrpc_async_call( 'jetpack.updateRole', $user_id, $signed_role );
+		\Jetpack::xmlrpc_async_call( 'jetpack.updateRole', $user_id, $signed_role );
 	}
 
 	static function maybe_demote_master_user( $user_id ) {
-		$master_user_id = Jetpack_Options::get_option( 'master_user' );
+		$master_user_id = \Jetpack_Options::get_option( 'master_user' );
 		$role           = self::get_role( $user_id );
 		if ( $user_id == $master_user_id && 'administrator' != $role ) {
-			$query      = new WP_User_Query(
+			$query      = new \WP_User_Query(
 				array(
 					'fields'  => array( 'id' ),
 					'role'    => 'administrator',
@@ -64,18 +66,18 @@ static function maybe_demote_master_user( $user_id ) {
 			$new_master = false;
 			foreach ( $query->results as $result ) {
 				$found_user_id = absint( $result->id );
-				if ( $found_user_id && Jetpack::is_user_connected( $found_user_id ) ) {
+				if ( $found_user_id && \Jetpack::is_user_connected( $found_user_id ) ) {
 					$new_master = $found_user_id;
 					break;
 				}
 			}
 
 			if ( $new_master ) {
-				Jetpack_Options::update_option( 'master_user', $new_master );
+				\Jetpack_Options::update_option( 'master_user', $new_master );
 			}
 			// else disconnect..?
 		}
 	}
 }
 
-Jetpack_Sync_Users::init();
+Users::init();
diff --git a/packages/sync/src/Utils.php b/packages/sync/src/Utils.php
new file mode 100644
index 000000000000..8417030a61f8
--- /dev/null
+++ b/packages/sync/src/Utils.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace Automattic\Jetpack\Sync;
+
+class Utils {
+	static function get_item_values( $items ) {
+		return array_map( array( __CLASS__, 'get_item_value' ), $items );
+	}
+
+	static function get_item_ids( $items ) {
+		return array_map( array( __CLASS__, 'get_item_id' ), $items );
+	}
+
+	private static function get_item_value( $item ) {
+		return $item->value;
+	}
+
+	private static function get_item_id( $item ) {
+		return $item->id;
+	}
+}
diff --git a/sync/class.jetpack-sync-wp-replicastore.php b/packages/sync/src/WP_Replicastore.php
similarity index 88%
rename from sync/class.jetpack-sync-wp-replicastore.php
rename to packages/sync/src/WP_Replicastore.php
index 99826bd08712..f38d0ee0625d 100644
--- a/sync/class.jetpack-sync-wp-replicastore.php
+++ b/packages/sync/src/WP_Replicastore.php
@@ -1,15 +1,12 @@
 <?php
 
-require_once dirname( __FILE__ ) . '/interface.jetpack-sync-replicastore.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-defaults.php';
+namespace Automattic\Jetpack\Sync;
 
 /**
- * An implementation of iJetpack_Sync_Replicastore which returns data stored in a WordPress.org DB.
+ * An implementation of Replicastore which returns data stored in a WordPress.org DB.
  * This is useful to compare values in the local WP DB to values in the synced replica store
  */
-class Jetpack_Sync_WP_Replicastore implements iJetpack_Sync_Replicastore {
-
-
+class WP_Replicastore implements Replicastore {
 	public function reset() {
 		global $wpdb;
 
@@ -86,7 +83,7 @@ public function upsert_post( $post, $silent = false ) {
 		global $wpdb;
 
 		// reject the post if it's not a WP_Post
-		if ( ! $post instanceof WP_Post ) {
+		if ( ! $post instanceof \WP_Post ) {
 			return;
 		}
 
@@ -148,12 +145,12 @@ public function delete_post( $post_id ) {
 
 	public function posts_checksum( $min_id = null, $max_id = null ) {
 		global $wpdb;
-		return $this->table_checksum( $wpdb->posts, Jetpack_Sync_Defaults::$default_post_checksum_columns, 'ID', Jetpack_Sync_Settings::get_blacklisted_post_types_sql(), $min_id, $max_id );
+		return $this->table_checksum( $wpdb->posts, Defaults::$default_post_checksum_columns, 'ID', Settings::get_blacklisted_post_types_sql(), $min_id, $max_id );
 	}
 
 	public function post_meta_checksum( $min_id = null, $max_id = null ) {
 		global $wpdb;
-		return $this->table_checksum( $wpdb->postmeta, Jetpack_Sync_Defaults::$default_post_meta_checksum_columns, 'meta_id', Jetpack_Sync_Settings::get_whitelisted_post_meta_sql(), $min_id, $max_id );
+		return $this->table_checksum( $wpdb->postmeta, Defaults::$default_post_meta_checksum_columns, 'meta_id', Settings::get_whitelisted_post_meta_sql(), $min_id, $max_id );
 	}
 
 	public function comment_count( $status = null, $min_id = null, $max_id = null ) {
@@ -283,21 +280,21 @@ public function untrashed_post_comments( $post_id ) {
 
 	public function comments_checksum( $min_id = null, $max_id = null ) {
 		global $wpdb;
-		return $this->table_checksum( $wpdb->comments, Jetpack_Sync_Defaults::$default_comment_checksum_columns, 'comment_ID', Jetpack_Sync_Settings::get_comments_filter_sql(), $min_id, $max_id );
+		return $this->table_checksum( $wpdb->comments, Defaults::$default_comment_checksum_columns, 'comment_ID', Settings::get_comments_filter_sql(), $min_id, $max_id );
 	}
 
 	public function comment_meta_checksum( $min_id = null, $max_id = null ) {
 		global $wpdb;
-		return $this->table_checksum( $wpdb->commentmeta, Jetpack_Sync_Defaults::$default_comment_meta_checksum_columns, 'meta_id', Jetpack_Sync_Settings::get_whitelisted_comment_meta_sql(), $min_id, $max_id );
+		return $this->table_checksum( $wpdb->commentmeta, Defaults::$default_comment_meta_checksum_columns, 'meta_id', Settings::get_whitelisted_comment_meta_sql(), $min_id, $max_id );
 	}
 
 	public function options_checksum() {
 		global $wpdb;
 
-		$options_whitelist = "'" . implode( "', '", Jetpack_Sync_Defaults::$default_options_whitelist ) . "'";
+		$options_whitelist = "'" . implode( "', '", Defaults::$default_options_whitelist ) . "'";
 		$where_sql         = "option_name IN ( $options_whitelist )";
 
-		return $this->table_checksum( $wpdb->options, Jetpack_Sync_Defaults::$default_option_checksum_columns, null, $where_sql, null, null );
+		return $this->table_checksum( $wpdb->options, Defaults::$default_option_checksum_columns, null, $where_sql, null, null );
 	}
 
 
@@ -495,7 +492,7 @@ private function ensure_taxonomy( $taxonomy ) {
 			$taxonomies = $this->get_callable( 'taxonomies' );
 			if ( ! isset( $taxonomies[ $taxonomy ] ) ) {
 				// doesn't exist, or somehow hasn't been synced
-				return new WP_Error( 'invalid_taxonomy', "The taxonomy '$taxonomy' doesn't exist" );
+				return new \WP_Error( 'invalid_taxonomy', "The taxonomy '$taxonomy' doesn't exist" );
 			}
 			$t = $taxonomies[ $taxonomy ];
 
@@ -655,37 +652,37 @@ function checksum_histogram( $object_type, $buckets, $start_id = null, $end_id =
 				$object_count = $this->post_count( null, $start_id, $end_id );
 				$object_table = $wpdb->posts;
 				$id_field     = 'ID';
-				$where_sql    = Jetpack_Sync_Settings::get_blacklisted_post_types_sql();
+				$where_sql    = Settings::get_blacklisted_post_types_sql();
 				if ( empty( $columns ) ) {
-					$columns = Jetpack_Sync_Defaults::$default_post_checksum_columns;
+					$columns = Defaults::$default_post_checksum_columns;
 				}
 				break;
 			case 'post_meta':
 				$object_table = $wpdb->postmeta;
-				$where_sql    = Jetpack_Sync_Settings::get_whitelisted_post_meta_sql();
+				$where_sql    = Settings::get_whitelisted_post_meta_sql();
 				$object_count = $this->meta_count( $object_table, $where_sql, $start_id, $end_id );
 				$id_field     = 'meta_id';
 
 				if ( empty( $columns ) ) {
-					$columns = Jetpack_Sync_Defaults::$default_post_meta_checksum_columns;
+					$columns = Defaults::$default_post_meta_checksum_columns;
 				}
 				break;
 			case 'comments':
 				$object_count = $this->comment_count( null, $start_id, $end_id );
 				$object_table = $wpdb->comments;
 				$id_field     = 'comment_ID';
-				$where_sql    = Jetpack_Sync_Settings::get_comments_filter_sql();
+				$where_sql    = Settings::get_comments_filter_sql();
 				if ( empty( $columns ) ) {
-					$columns = Jetpack_Sync_Defaults::$default_comment_checksum_columns;
+					$columns = Defaults::$default_comment_checksum_columns;
 				}
 				break;
 			case 'comment_meta':
 				$object_table = $wpdb->commentmeta;
-				$where_sql    = Jetpack_Sync_Settings::get_whitelisted_comment_meta_sql();
+				$where_sql    = Settings::get_whitelisted_comment_meta_sql();
 				$object_count = $this->meta_count( $object_table, $where_sql, $start_id, $end_id );
 				$id_field     = 'meta_id';
 				if ( empty( $columns ) ) {
-					$columns = Jetpack_Sync_Defaults::$default_post_meta_checksum_columns;
+					$columns = Defaults::$default_post_meta_checksum_columns;
 				}
 				break;
 			default:
@@ -712,7 +709,7 @@ function checksum_histogram( $object_type, $buckets, $start_id = null, $end_id =
 				ARRAY_N
 			);
 
-			if ( null === $first_id || null === $last_id  ) {
+			if ( null === $first_id || null === $last_id ) {
 				// Nothing to checksum here...
 				break;
 			}
@@ -724,7 +721,7 @@ function checksum_histogram( $object_type, $buckets, $start_id = null, $end_id =
 				return $value;
 			}
 
-			if ( null === $first_id || null === $last_id  ) {
+			if ( null === $first_id || null === $last_id ) {
 				break;
 			} elseif ( $first_id === $last_id ) {
 				$histogram[ $first_id ] = $value;
@@ -752,34 +749,34 @@ private function table_checksum( $table, $columns, $id_column, $where_sql = '1=1
 
 		if ( null !== $min_id && null !== $max_id ) {
 			if ( $min_id === $max_id ) {
-				$min_id = intval( $min_id );
+				$min_id     = intval( $min_id );
 				$where_sql .= " AND $id_column = $min_id LIMIT 1";
 			} else {
-				$min_id = intval( $min_id );
-				$max_id = intval( $max_id );
-				$size = $max_id - $min_id;
+				$min_id     = intval( $min_id );
+				$max_id     = intval( $max_id );
+				$size       = $max_id - $min_id;
 				$where_sql .= " AND $id_column >= $min_id AND $id_column <= $max_id LIMIT $size";
 			}
 		} else {
 			if ( null !== $min_id ) {
-				$min_id = intval( $min_id );
+				$min_id     = intval( $min_id );
 				$where_sql .= " AND $id_column >= $min_id";
 			}
 
 			if ( null !== $max_id ) {
-				$max_id = intval( $max_id );
+				$max_id     = intval( $max_id );
 				$where_sql .= " AND $id_column <= $max_id";
 			}
 		}
 
-		$query = <<<ENDSQL
+		$query  = <<<ENDSQL
 			SELECT CAST( SUM( CRC32( CONCAT_WS( '#', '%s', {$columns_sql} ) ) ) AS UNSIGNED INT )
 			FROM $table
 			WHERE $where_sql;
 ENDSQL;
 		$result = $wpdb->get_var( $wpdb->prepare( $query, $salt ) );
 		if ( $wpdb->last_error ) {
-			return new WP_Error( 'database_error', $wpdb->last_error );
+			return new \WP_Error( 'database_error', $wpdb->last_error );
 		}
 
 		return $result;
diff --git a/sal/class.json-api-site-jetpack.php b/sal/class.json-api-site-jetpack.php
index 0efcb3aadb1f..c1cd02bccc3a 100644
--- a/sal/class.json-api-site-jetpack.php
+++ b/sal/class.json-api-site-jetpack.php
@@ -1,5 +1,7 @@
 <?php
 
+use Automattic\Jetpack\Sync\Functions;
+
 require_once dirname( __FILE__ ) . '/class.json-api-site-jetpack-base.php';
 require_once dirname( __FILE__ ) . '/class.json-api-post-jetpack.php';
 
@@ -51,11 +53,11 @@ public function is_single_user_site() {
 	}
 
 	protected function is_version_controlled() {
-		return Jetpack_Sync_Functions::is_version_controlled();
+		return Functions::is_version_controlled();
 	}
 
 	protected function file_system_write_access() {
-		return Jetpack_Sync_Functions::file_system_write_access();
+		return Functions::file_system_write_access();
 	}
 
 	protected function current_theme_supports( $feature_name ) {
diff --git a/sync/class.jetpack-sync-modules.php b/sync/class.jetpack-sync-modules.php
deleted file mode 100644
index 2450bae9a3d2..000000000000
--- a/sync/class.jetpack-sync-modules.php
+++ /dev/null
@@ -1,104 +0,0 @@
-<?php
-
-/**
- * simple wrapper that allows enumerating cached static instances
- * of sync modules
- */
-
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-posts.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-import.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-comments.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-constants.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-callables.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-options.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-network-options.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-updates.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-users.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-themes.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-menus.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-attachments.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-meta.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-terms.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-plugins.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-full-sync.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-stats.php';
-require_once dirname( __FILE__ ) . '/class.jetpack-sync-module-protect.php';
-
-class Jetpack_Sync_Modules {
-
-	private static $default_sync_modules = array(
-		'Jetpack_Sync_Module_Constants',
-		'Jetpack_Sync_Module_Callables',
-		'Jetpack_Sync_Module_Options',
-		'Jetpack_Sync_Module_Network_Options',
-		'Jetpack_Sync_Module_Terms',
-		'Jetpack_Sync_Module_Themes',
-		'Jetpack_Sync_Module_Menus',
-		'Jetpack_Sync_Module_Users',
-		'Jetpack_Sync_Module_Posts',
-		'Jetpack_Sync_Module_Import',
-		'Jetpack_Sync_Module_Protect',
-		'Jetpack_Sync_Module_Comments',
-		'Jetpack_Sync_Module_Updates',
-		'Jetpack_Sync_Module_Attachments',
-		'Jetpack_Sync_Module_Meta',
-		'Jetpack_Sync_Module_Plugins',
-		'Jetpack_Sync_Module_Full_Sync',
-		'Jetpack_Sync_Module_Stats',
-	);
-
-	private static $initialized_modules = null;
-
-	public static function get_modules() {
-		if ( null === self::$initialized_modules ) {
-			self::$initialized_modules = self::initialize_modules();
-		}
-
-		return self::$initialized_modules;
-	}
-
-	public static function set_defaults() {
-		foreach ( self::get_modules() as $module ) {
-			$module->set_defaults();
-		}
-	}
-
-	public static function get_module( $module_name ) {
-		foreach ( self::get_modules() as $module ) {
-			if ( $module->name() === $module_name ) {
-				return $module;
-			}
-		}
-
-		return false;
-	}
-
-	static function initialize_modules() {
-		/**
-		 * Filters the list of class names of sync modules.
-		 * If you add to this list, make sure any classes implement the
-		 * Jetpack_Sync_Module interface.
-		 *
-		 * @since 4.2.0
-		 */
-		$modules = apply_filters( 'jetpack_sync_modules', self::$default_sync_modules );
-
-		$modules = array_map( array( 'Jetpack_Sync_Modules', 'load_module' ), $modules );
-
-		return array_map( array( 'Jetpack_Sync_Modules', 'set_module_defaults' ), $modules );
-	}
-
-	static function load_module( $module_name ) {
-		return new $module_name();
-	}
-
-	static function set_module_defaults( $module ) {
-		$module->set_defaults();
-		if ( method_exists( $module, 'set_late_default' ) ) {
-			add_action( 'init', array( $module, 'set_late_default' ), 90 );
-		}
-		return $module;
-	}
-
-}
diff --git a/uninstall.php b/uninstall.php
index 366e62d13632..64a025c086c1 100644
--- a/uninstall.php
+++ b/uninstall.php
@@ -1,5 +1,7 @@
 <?php
 
+use Automattic\Jetpack\Sync\Sender;
+
 if (
 	!defined( 'WP_UNINSTALL_PLUGIN' )
 	||
@@ -32,5 +34,4 @@
 add_filter( 'jetpack_sync_modules', '__return_empty_array', 100 );
 
 // Jetpack Sync
-require_once JETPACK__PLUGIN_DIR . 'sync/class.jetpack-sync-sender.php';
-Jetpack_Sync_Sender::get_instance()->uninstall();
+Sender::get_instance()->uninstall();