diff --git a/.circleci/config.yml b/.circleci/config.yml
index 0bc24fa6..5cea19af 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -3,7 +3,7 @@ version: 2
 jobs:
   build:
     docker:
-      - image: googleapis/nox:0.17.0
+      - image: gcr.io/cloud-devrel-public-resources/python
     steps:
       - checkout
       - run:
diff --git a/nox.py b/noxfile.py
similarity index 83%
rename from nox.py
rename to noxfile.py
index e0ed0437..4a015d8f 100644
--- a/nox.py
+++ b/noxfile.py
@@ -26,14 +26,10 @@
 GOOGLE_AUTH = 'google-auth >= 0.10.0'
 
 
-@nox.session
-@nox.parametrize('python_version', ['2.7', '3.4', '3.5', '3.6'])
-def unit_tests(session, python_version):
+@nox.session(python=['2,7', '3.4', '3.5', '3.6', '3.7'])
+def unit_tests(session):
     """Run the unit test suite."""
 
-    # Run unit tests against all supported versions of Python.
-    session.interpreter = 'python{}'.format(python_version)
-
     # Install all test dependencies, then install this package in-place.
     session.install('mock', 'pytest', 'pytest-cov', REQUESTS)
     session.install('-e', '.')
@@ -55,13 +51,10 @@ def unit_tests(session, python_version):
     )
 
 
-@nox.session
+@nox.session(python='3.6')
 def docs(session):
     """Build the docs."""
 
-    # Build docs against the latest version of Python, because we can.
-    session.interpreter = 'python3.6'
-
     # Install Sphinx and other dependencies.
     session.chdir(os.path.realpath(os.path.dirname(__file__)))
     session.install(
@@ -76,11 +69,9 @@ def docs(session):
     session.run('bash', os.path.join('scripts', 'build_docs.sh'))
 
 
-@nox.session
+@nox.session(python='3.6')
 def doctest(session):
     """Run the doctests."""
-    session.interpreter = 'python3.6'
-
     # Install Sphinx and other dependencies.
     session.chdir(os.path.realpath(os.path.dirname(__file__)))
     session.install(
@@ -101,14 +92,13 @@ def doctest(session):
     )
 
 
-@nox.session
+@nox.session(python='3.6')
 def lint(session):
     """Run flake8.
 
     Returns a failure if flake8 finds linting errors or sufficiently
     serious code quality issues.
     """
-    session.interpreter = 'python3.6'
     session.install('flake8')
     session.install('-e', '.')
     session.run(
@@ -118,18 +108,16 @@ def lint(session):
     )
 
 
-@nox.session
+@nox.session(python='3.6')
 def lint_setup_py(session):
     """Verify that setup.py is valid (including RST check)."""
-    session.interpreter = 'python3.6'
     session.install('docutils', 'Pygments')
     session.run(
         'python', 'setup.py', 'check', '--restructuredtext', '--strict')
 
 
-@nox.session
-@nox.parametrize('python_version', ['2.7', '3.6'])
-def system_tests(session, python_version):
+@nox.session(python=['2.7', '3.6'])
+def system_tests(session):
     """Run the system test suite."""
 
     # Sanity check: environment variables are set.
@@ -144,9 +132,6 @@ def system_tests(session, python_version):
         msg = 'Environment variable(s) unset: {}'.format(all_vars)
         session.skip(msg)
 
-    # Run the system tests against latest Python 2 and Python 3 only.
-    session.interpreter = 'python{}'.format(python_version)
-
     # Install all test dependencies, then install this package into the
     # virutalenv's dist-packages.
     session.install('mock', 'pytest', REQUESTS, GOOGLE_AUTH)
@@ -160,14 +145,13 @@ def system_tests(session, python_version):
     )
 
 
-@nox.session
+@nox.session(python='3.6')
 def cover(session):
     """Run the final coverage report.
 
     This outputs the coverage report aggregating coverage from the unit
     test runs (not system test runs), and then erases coverage data.
     """
-    session.interpreter = 'python3.6'
     session.install('coverage', 'pytest-cov')
     session.run('coverage', 'report', '--show-missing', '--fail-under=100')
     session.run('coverage', 'erase')