diff --git a/.github/workflows/benchmark.yml b/.github/workflows/benchmark.yml
index 5be56c1d80..d0bcd342cb 100644
--- a/.github/workflows/benchmark.yml
+++ b/.github/workflows/benchmark.yml
@@ -28,7 +28,7 @@ jobs:
       IRIS_TEST_DATA_PATH: benchmarks/iris-test-data
       IRIS_TEST_DATA_VERSION: "2.19"
       # Lets us manually bump the cache to rebuild
-      ENV_CACHE_BUILD: "0"
+      ENV_CACHE_BUILD: "1"
       TEST_DATA_CACHE_BUILD: "2"
 
     steps:
@@ -37,16 +37,16 @@ jobs:
         with:
           fetch-depth: 0
 
-      - name: Install ASV & Nox
+      - name: Install ASV & tox
         run: |
-          pip install asv nox
+          pip install asv tox
 
       - name: Cache environment directories
         id: cache-env-dir
         uses: actions/cache@v3
         with:
           path: |
-            .nox
+            .tox
             benchmarks/.asv/env
             $CONDA/pkgs
           key: ${{ runner.os }}-${{ hashFiles('requirements/') }}-${{ env.ENV_CACHE_BUILD }}
diff --git a/.github/workflows/ci-tests.yml b/.github/workflows/ci-tests.yml
index 5c48966ce8..04a3d11ead 100644
--- a/.github/workflows/ci-tests.yml
+++ b/.github/workflows/ci-tests.yml
@@ -35,18 +35,18 @@ jobs:
       fail-fast: false
       matrix:
         os: ["ubuntu-latest"]
-        python-version: ["3.11"]
-        session: ["doctest", "gallery", "linkcheck"]
+        python-version: ["311"]
+        session: ["docs-tests", "docs-linkcheck", "gallery_tests"]
         include:
           - os: "ubuntu-latest"
-            python-version: "3.11"
+            python-version: "311"
             session: "tests"
-            coverage: "--coverage"
+            posargs: "--cov=lib/iris --cov-report=xml"
           - os: "ubuntu-latest"
-            python-version: "3.10"
+            python-version: "310"
             session: "tests"
           - os: "ubuntu-latest"
-            python-version: "3.9"
+            python-version: "39"
             session: "tests"
 
     env:
@@ -63,7 +63,7 @@ jobs:
           CACHE_WEEKS: 2
         run: |
           echo "CACHE_PERIOD=$(date +%Y).$(expr $(date +%U) / ${CACHE_WEEKS})" >> ${GITHUB_ENV}
-          echo "LOCK_FILE=requirements/locks/py$(echo ${{ matrix.python-version }} | tr -d '.')-linux-64.lock" >> ${GITHUB_ENV}
+          echo "LOCK_FILE=requirements/locks/py$(echo ${{ matrix.python-version }})-linux-64.lock" >> ${GITHUB_ENV}
 
       - name: "data cache"
         uses: ./.github/workflows/composite/iris-data-cache
@@ -91,10 +91,10 @@ jobs:
       - name: "conda environment cache"
         uses: ./.github/workflows/composite/conda-env-cache
         with:
-          cache_build: 0
+          cache_build: 1
           cache_period: ${{ env.CACHE_PERIOD }}
           env_name: ${{ env.ENV_NAME }}
-          install_packages: "cartopy nox pip"
+          install_packages: "cartopy tox'<4'"
 
       - name: "conda info"
         run: |
@@ -108,8 +108,8 @@ jobs:
           cache_period: ${{ env.CACHE_PERIOD }}
           env_name: ${{ env.ENV_NAME }}
 
-      - name: "nox cache"
-        uses: ./.github/workflows/composite/nox-cache
+      - name: "tox cache"
+        uses: ./.github/workflows/composite/tox-cache
         with:
           cache_build: 2
           env_name: ${{ env.ENV_NAME }}
@@ -134,11 +134,9 @@ jobs:
           cat ${MPL_RC}
 
       - name: "iris ${{ matrix.session }}"
-        env:
-          PY_VER: ${{ matrix.python-version }}
         run: |
-          nox --session ${{ matrix.session }} -- --verbose ${{ matrix.coverage }}
+            tox -e py${{ matrix.python-version }}-${{ matrix.session }} -- ${{ matrix.posargs }}
 
       - name: Upload coverage report
         uses: codecov/codecov-action@v3
-        if: ${{ matrix.coverage }}
+        if: contains(${{ matrix.posargs }}, "--cov=lib/iris --cov-report=xml")
diff --git a/.github/workflows/ci-wheels.yml b/.github/workflows/ci-wheels.yml
index 942d528f6d..6b585c7d98 100644
--- a/.github/workflows/ci-wheels.yml
+++ b/.github/workflows/ci-wheels.yml
@@ -52,7 +52,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.9", "3.10", "3.11"]
+        python-version: ["39", "310", "311"]
         session: ["wheel"]
     env:
       ENV_NAME: "ci-wheels"
@@ -72,7 +72,7 @@ jobs:
           CACHE_WEEKS: 2
       run: |
         echo "CACHE_PERIOD=$(date +%Y).$(expr $(date +%U) / ${CACHE_WEEKS})" >> ${GITHUB_ENV}
-        echo "LOCK_FILE=requirements/locks/py$(echo ${{ matrix.python-version }} | tr -d '.')-linux-64.lock" >> ${GITHUB_ENV}
+        echo "LOCK_FILE=requirements/locks/py$(echo ${{ matrix.python-version }})-linux-64.lock" >> ${GITHUB_ENV}
 
     - name: "conda package cache"
       uses: ./.github/workflows/composite/conda-pkg-cache
@@ -93,23 +93,21 @@ jobs:
     - name: "conda environment cache"
       uses: ./.github/workflows/composite/conda-env-cache
       with:
-        cache_build: 0
+        cache_build: 1
         cache_period: ${{ env.CACHE_PERIOD }}
         env_name: ${{ env.ENV_NAME }}
-        install_packages: "nox pip"
+        install_packages: "tox'<4' pip"
 
-    - name: "nox cache"
-      uses: ./.github/workflows/composite/nox-cache
+    - name: "tox cache"
+      uses: ./.github/workflows/composite/tox-cache
       with:
         cache_build: 1
         env_name: ${{ env.ENV_NAME }}
         lock_file: ${{ env.LOCK_FILE }}
 
-    - name: "nox install and test wheel"
-      env:
-        PY_VER: ${{ matrix.python-version }}
+    - name: "tox install and test wheel"
       run: |
-        nox --session ${{ matrix.session }} -- --verbose
+        tox -e py${{ matrix.python-version }}-${{ matrix.session }}
 
   show-artifacts:
     needs: build
diff --git a/.github/workflows/composite/nox-cache/action.yml b/.github/workflows/composite/tox-cache/action.yml
similarity index 65%
rename from .github/workflows/composite/nox-cache/action.yml
rename to .github/workflows/composite/tox-cache/action.yml
index 468dd22d81..48962f9d51 100644
--- a/.github/workflows/composite/nox-cache/action.yml
+++ b/.github/workflows/composite/tox-cache/action.yml
@@ -1,9 +1,9 @@
-name: "nox cache"
-description: "cache the nox test environments"
+name: "tox cache"
+description: "cache the tox test environments"
 
 inputs:
   cache_build:
-    description: "nox cache build number"
+    description: "tox cache build number"
     required: false
     default: "0"
   env_name:
@@ -18,5 +18,5 @@ runs:
   steps:
     - uses: actions/cache@v3
       with:
-        path: ${{ github.workspace }}/.nox
-        key: ${{ runner.os }}-nox-${{ inputs.env_name }}-s${{ matrix.session }}-py${{ matrix.python-version }}-b${{ inputs.cache_build }}-${{ hashFiles(inputs.lock_file) }}
+        path: ${{ github.workspace }}/.tox
+        key: ${{ runner.os }}-tox-${{ inputs.env_name }}-s${{ matrix.session }}-py${{ matrix.python-version }}-b${{ inputs.cache_build }}-${{ hashFiles(inputs.lock_file) }}
diff --git a/MANIFEST.in b/MANIFEST.in
index 329cf79c5d..abfbba5a5e 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -20,7 +20,7 @@ exclude codecov.yml
 include COPYING
 include COPYING.LESSER
 exclude Makefile
-exclude noxfile.py
+exclude tox.ini
 
 # files required to build iris.std_names module
 include etc/cf-standard-name-table.xml
diff --git a/benchmarks/README.md b/benchmarks/README.md
index 316c8f9e32..e0147c0bc2 100644
--- a/benchmarks/README.md
+++ b/benchmarks/README.md
@@ -21,7 +21,7 @@ by the PR. (This run is managed by
 [the aforementioned GitHub Action](../.github/workflows/benchmark.yml)).
 
 `asv ...` commands must be run from this directory. You will need to have ASV
-installed, as well as Nox (see
+installed, as well as tox (see
 [Benchmark environments](#benchmark-environments)).
 
 The benchmark runner ([bm_runner.py](./bm_runner.py)) provides conveniences for
@@ -107,8 +107,7 @@ suites for the UK Met Office NG-VAT project.
 ## Benchmark environments
 
 We have disabled ASV's standard environment management, instead using an
-environment built using the same Nox scripts as Iris' test environments. This
-is done using ASV's plugin architecture - see
+environment built using tox. This is done using ASV's plugin architecture - see
 [asv_delegated_conda.py](asv_delegated_conda.py) and the extra config items in
 [asv.conf.json](asv.conf.json).
 
@@ -116,4 +115,4 @@ is done using ASV's plugin architecture - see
 minimising external factors and also allowing it to compare between a matrix
 of dependencies (each in a separate environment). We have chosen to sacrifice
 these features in favour of testing each commit with its intended dependencies,
-controlled by Nox + lock-files).
+controlled by tox + lock-files).
diff --git a/benchmarks/asv.conf.json b/benchmarks/asv.conf.json
index faa7f6daee..f088685b24 100644
--- a/benchmarks/asv.conf.json
+++ b/benchmarks/asv.conf.json
@@ -20,9 +20,9 @@
     //  * No build-time environment variables.
     //  * Is run in the same environment as the ASV install itself.
     "delegated_env_commands": [
-        "PY_VER=3.11 nox --envdir={conf_dir}/.asv/env/nox01 --session=tests --install-only --no-error-on-external-run --verbose"
+        "tox -c {conf_dir}/.. --devenv={conf_dir}/.asv/env/tox01/bm_env -e py311 --verbose"
     ],
     // The parent directory of the above environment.
     //  The most recently modified environment in the directory will be used.
-    "delegated_env_parent": "{conf_dir}/.asv/env/nox01"
+    "delegated_env_parent": "{conf_dir}/.asv/env/tox01"
 }
diff --git a/benchmarks/bm_runner.py b/benchmarks/bm_runner.py
index f3efb0ea31..38e5a6c806 100644
--- a/benchmarks/bm_runner.py
+++ b/benchmarks/bm_runner.py
@@ -62,27 +62,29 @@ def _prep_data_gen_env() -> None:
     """
 
     root_dir = BENCHMARKS_DIR.parent
-    python_version = "3.11"
+    python_version = "311"
     data_gen_var = "DATA_GEN_PYTHON"
     if data_gen_var in environ:
         print("Using existing data generation environment.")
     else:
         print("Setting up the data generation environment ...")
-        # Get Nox to build an environment for the `tests` session, but don't
-        #  run the session. Will re-use a cached environment if appropriate.
+        # Get tox to build an environment. It will re-use a cached environment
+        # if appropriate.
         _subprocess_run_print(
             [
-                "nox",
-                f"--noxfile={root_dir / 'noxfile.py'}",
-                "--session=tests",
-                "--install-only",
-                f"--python={python_version}",
+                "tox",
+                "-c",
+                str(root_dir),
+                "-e",
+                f"py{python_version}",
             ]
         )
         # Find the environment built above, set it to be the data generation
         #  environment.
         data_gen_python = next(
-            (root_dir / ".nox").rglob(f"tests*/bin/python{python_version}")
+            (root_dir / ".tox").rglob(
+                f"py{python_version}/bin/python{python_version[:1]}.{python_version[1:]}"
+            )
         ).resolve()
         environ[data_gen_var] = str(data_gen_python)
 
@@ -112,7 +114,7 @@ def _prep_data_gen_env() -> None:
 
 def _setup_common() -> None:
     _check_requirements("asv")
-    _check_requirements("nox")
+    _check_requirements("tox")
 
     _prep_data_gen_env()
 
@@ -154,7 +156,7 @@ def _asv_compare(*commits: str, overnight_mode: bool = False) -> None:
 
 
 class _SubParserGenerator(ABC):
-    """Convenience for holding all the necessary argparse info in 1 place."""
+    """Convenience for holding all the necessary argparse info in one place."""
 
     name: str = NotImplemented
     description: str = NotImplemented
diff --git a/docs/src/common_links.inc b/docs/src/common_links.inc
index ba24141d87..c807eeff93 100644
--- a/docs/src/common_links.inc
+++ b/docs/src/common_links.inc
@@ -37,6 +37,7 @@
 .. _sphinx: https://www.sphinx-doc.org/en/master/
 .. _sphinx-apidoc: https://github.com/sphinx-contrib/apidoc
 .. _test-iris-imagehash: https://github.com/SciTools/test-iris-imagehash
+.. _tox: https://tox.readthedocs.io/en/latest/
 .. _using git: https://docs.github.com/en/github/using-git
 .. _requirements: https://github.com/SciTools/iris/tree/main/requirements
 .. _CF-UGRID: https://ugrid-conventions.github.io/ugrid-conventions/
diff --git a/docs/src/conf.py b/docs/src/conf.py
index a204263a24..d7c04f2130 100644
--- a/docs/src/conf.py
+++ b/docs/src/conf.py
@@ -384,6 +384,7 @@ def _dotv(version):
     "http://www.nationalarchives.gov.uk/doc/open-government-licence",
     "https://www.metoffice.gov.uk/",
     "https://biggus.readthedocs.io/",
+    "https://stickler-ci.com/",
 ]
 
 # list of sources to exclude from the build.
diff --git a/docs/src/developers_guide/contributing_pull_request_checklist.rst b/docs/src/developers_guide/contributing_pull_request_checklist.rst
index 11d68ace46..74002e7325 100644
--- a/docs/src/developers_guide/contributing_pull_request_checklist.rst
+++ b/docs/src/developers_guide/contributing_pull_request_checklist.rst
@@ -30,7 +30,7 @@ is merged.  Before submitting a pull request please consider the following:
    :ref:`code_formatting`.
 
 #. **Check all new dependencies added to the** `requirements`_ **yaml
-   files.**  If dependencies have been added then new nox testing lockfiles
+   files.**  If dependencies have been added then new testing lockfiles
    should be generated too, see :ref:`gha_test_env`.
 
 #. **Check the source documentation been updated to explain all new or changed
diff --git a/docs/src/developers_guide/contributing_running_tests.rst b/docs/src/developers_guide/contributing_running_tests.rst
index f60cedba05..fdf8530566 100644
--- a/docs/src/developers_guide/contributing_running_tests.rst
+++ b/docs/src/developers_guide/contributing_running_tests.rst
@@ -12,8 +12,8 @@ There are two options for running the tests:
   the tests or use ``python`` interactively to investigate any issues.  See
   :ref:`test manual env`.
 
-* Use ``nox``.  This will automatically generate an environment and run test
-  sessions consistent with our GitHub continuous integration.  See :ref:`using nox`.
+* Use ``tox``.  This will automatically generate an environment and run test
+  sessions consistent with our GitHub continuous integration.  See :ref:`using tox`.
 
 .. _test manual env:
 
@@ -101,97 +101,84 @@ using the commands ``python test_mapping.py -h`` or
 ``python test_mapping.py --help``.
 
 .. tip::  A useful command line option to use is ``-d``.  This will display
-          matplotlib_ figures as the tests are run.  For example::
+          `matplotlib_` figures as the tests are run.  For example::
 
              python test_mapping.py -d
 
-.. _using nox:
+.. _using tox:
 
-Using Nox for Testing Iris
+Using tox for Testing Iris
 ==========================
 
-The `nox`_ tool has for adopted for automated testing on `Iris GitHub Actions`_
+The `tox`_ tool has been adopted for automated testing on `Iris GitHub Actions`_
 and also locally on the command-line for developers.
 
-`nox`_ is similar to `tox`_, but instead leverages the expressiveness and power of a Python
-configuration file rather than an `.ini` style file. As with `tox`_, `nox`_ can use `virtualenv`_
-to create isolated Python environments, but in addition also supports `conda`_ as a testing
-environment backend.
+`tox`_ uses `virtualenv`_ to create isolated Python environments and is
+configured within a tox.ini file.
 
-
-Where is Nox Used?
+Where is tox Used?
 ------------------
 
-Iris uses `nox`_ as a convenience to fully automate the process of executing the Iris tests, but also
-automates the process of:
+Iris uses `tox`_ as a convenience to fully automate the process of:
 
-* building the documentation and executing the doc-tests
-* building the documentation gallery
+* executing the Iris tests,
+* building the documentation,
+* executing the doc-tests,
+* executing the gallery tests, and
 * running the documentation URL link check
 
-You can perform all of these tasks manually yourself, however the onus is on you to first ensure
-that all of the required package dependencies are installed and available in the testing environment.
+You can perform all of these tasks manually yourself, however the onus is on you
+to first ensure that all of the required package dependencies are installed and
+available in the testing environment.
 
-`Nox`_ has been configured to automatically do this for you, and provides a means to easily replicate
-the remote testing behaviour of `Iris GitHub Actions`_ locally for the developer.
+`tox`_ has been configured to automatically do this for you, and provides a
+means to easily replicate the remote testing behaviour of `Iris GitHub Actions`_
+locally for the developer.
 
 
-Installing Nox
+Installing tox
 --------------
 
-We recommend installing `nox`_ using `conda`_. To install `nox`_ in a separate `conda`_ environment::
+We recommend installing `tox`_ using `conda`_. To install `tox`_ in a separate
+`conda`_ environment::
 
-  conda create -n nox -c conda-forge nox
-  conda activate nox
+  conda create -n tox -c conda-forge tox
+  conda activate tox
 
-To install `nox`_ in an existing active `conda`_ environment::
+To install `tox`_ in an existing active `conda`_ environment::
 
-  conda install -c conda-forge nox
+  conda install -c conda-forge tox
 
-The `nox`_ package is also available on PyPI, however `nox`_ has been configured to use the `conda`_
-backend for Iris, so an installation of `conda`_ must always be available.
+The `tox`_ package is also available on PyPI, however `tox`_ has been configured
+to use `conda`_ to create the testing environments and so an installation of
+`conda`_ must always be available.
 
 
-Testing with Nox
+Testing with tox
 ----------------
 
-The `nox`_ configuration file `noxfile.py` is available in the root ``iris`` project directory, and
-defines all the `nox`_ sessions (i.e., tasks) that may be performed. `nox`_ must always be executed
-from the ``iris`` root directory.
-
-To list the configured `nox`_ sessions for Iris::
-
-  nox --list
-
-To run the Iris tests for all configured versions of Python::
+The `tox`_ configuration file `tox.ini` is available in the root ``iris``
+project directory, and defines all the `tox`_ test environments (i.e., tasks)
+that may be performed. `tox`_ must always be executed from the ``iris`` root
+directory.
 
-  nox --session tests
+To list the configured `tox`_ sessions for Iris::
 
-To build the Iris documentation specifically for Python 3.7::
+  tox --listenvs-all
 
-  nox --session doctest-3.7
+To run the Iris tests for Python 3.11::
 
-To run all the Iris `nox`_ sessions::
+  tox -e py311-tests
 
-  nox
+To build the Iris documentation specifically for Python 3.11::
 
-For further `nox`_ command-line options::
-
-  nox --help
-
-.. tip::
-    For `nox`_ sessions that use the `conda`_ backend, you can use the ``-v`` or ``--verbose``
-    flag to display the `nox`_ `conda`_ environment package details and environment info.
-    For example::
+  tox -e py311-docs
 
-        nox --session tests -- --verbose
+For further `tox`_ command-line options::
 
+  tox --help
 
-.. note:: `nox`_ will cache its testing environments in the `.nox` root ``iris`` project directory.
+.. note:: `tox`_ will cache its testing environments in the `.tox` root ``iris`` project directory.
 
 
-.. _setuptools: https://setuptools.readthedocs.io/en/latest/
-.. _tox: https://tox.readthedocs.io/en/latest/
-.. _virtualenv: https://virtualenv.pypa.io/en/latest/
-.. _PyPI: https://pypi.org/project/nox/
-.. _v41.5.0: https://setuptools.readthedocs.io/en/latest/history.html#v41-5-0
+.. _virtualenv: https://virtualenv.pypa.io/en/latest/
\ No newline at end of file
diff --git a/docs/src/whatsnew/latest.rst b/docs/src/whatsnew/latest.rst
index 9b62715be6..7a02fa492d 100644
--- a/docs/src/whatsnew/latest.rst
+++ b/docs/src/whatsnew/latest.rst
@@ -84,6 +84,9 @@ This document explains the changes made to Iris for this release
    `"Xarray bridge" <https://github.com/SciTools/iris/issues/4994>`_ facility.
    (:pull:`5214`)
 
+# `@lbdreyer`_ replaced nox with tox as the automated test runner.
+  (:pull:`5184`)
+
 
 .. comment
     Whatsnew author names (@github name) in alphabetical order. Note that,
diff --git a/lib/iris/tests/test_coding_standards.py b/lib/iris/tests/test_coding_standards.py
index 6cea9dc001..1431e1b59f 100644
--- a/lib/iris/tests/test_coding_standards.py
+++ b/lib/iris/tests/test_coding_standards.py
@@ -71,8 +71,8 @@ def test_python_versions():
     This test is designed to fail whenever Iris' supported Python versions are
     updated, insisting that versions are updated EVERYWHERE in-sync.
     """
-    latest_supported = "3.11"
-    all_supported = ["3.9", "3.10", latest_supported]
+    latest_supported = "311"
+    all_supported = ["39", "310", latest_supported]
 
     root_dir = Path(__file__).parents[3]
     workflows_dir = root_dir / ".github" / "workflows"
@@ -81,7 +81,7 @@ def test_python_versions():
     # Places that are checked:
     pyproject_toml_file = root_dir / "pyproject.toml"
     requirements_dir = root_dir / "requirements"
-    nox_file = root_dir / "noxfile.py"
+    tox_config_file = root_dir / "tox.ini"
     ci_wheels_file = workflows_dir / "ci-wheels.yml"
     ci_tests_file = workflows_dir / "ci-tests.yml"
     asv_config_file = benchmarks_dir / "asv.conf.json"
@@ -92,35 +92,35 @@ def test_python_versions():
             pyproject_toml_file,
             "\n    ".join(
                 [
-                    f'"Programming Language :: Python :: {ver}",'
+                    f'"Programming Language :: Python :: {ver[:1]}.{ver[1:]}",'
                     for ver in all_supported
                 ]
             ),
         ),
-        (
-            nox_file,
-            "_PY_VERSIONS_ALL = ["
-            + ", ".join([f'"{ver}"' for ver in all_supported]),
-        ),
         (
             ci_wheels_file,
             "python-version: ["
-            + ", ".join([f'"{ver}"' for ver in all_supported]),
+            + ", ".join([f'"{ver}"' for ver in all_supported])
+            + "]",
         ),
         (
             ci_tests_file,
             (
                 f'python-version: ["{latest_supported}"]\n'
-                f'{" " * 8}session: ["doctest", "gallery", "linkcheck"]'
+                f'{" " * 8}session: ["docs-tests", "docs-linkcheck", "gallery_tests"]'
             ),
         ),
-        (asv_config_file, f"PY_VER={latest_supported}"),
+        (
+            asv_config_file,
+            f"-e py{latest_supported}",
+        ),
         (benchmark_runner_file, f'python_version = "{latest_supported}"'),
+        (tox_config_file, "[testenv:py{" + ",".join(all_supported) + "}-"),
     ]
 
     for ver in all_supported:
-        req_yaml = requirements_dir / f"py{ver.replace('.', '')}.yml"
-        text_searches.append((req_yaml, f"- python ={ver}"))
+        req_yaml = requirements_dir / f"py{ver}.yml"
+        text_searches.append((req_yaml, f"- python ={ver[:1]}.{ver[1:]}"))
 
         text_searches.append(
             (
@@ -129,6 +129,13 @@ def test_python_versions():
             )
         )
 
+        text_searches.append(
+            (
+                tox_config_file,
+                f'{" " * 4}py{ver}: {{toxinidir}}{{/}}requirements',
+            )
+        )
+
     for path, search in text_searches:
         assert search in path.read_text()
 
@@ -194,7 +201,6 @@ def last_change_by_fname():
     def test_license_headers(self):
         exclude_patterns = (
             "setup.py",
-            "noxfile.py",
             "build/*",
             "dist/*",
             "docs/gallery_code/*/*.py",
diff --git a/lib/iris/tests/unit/analysis/stats/test_pearsonr.py b/lib/iris/tests/unit/analysis/stats/test_pearsonr.py
index 63cf4e2abe..5f5b76d9ac 100644
--- a/lib/iris/tests/unit/analysis/stats/test_pearsonr.py
+++ b/lib/iris/tests/unit/analysis/stats/test_pearsonr.py
@@ -36,11 +36,11 @@ def setUp(self):
 
     def test_perfect_corr(self):
         r = stats.pearsonr(self.cube_a, self.cube_a, ["latitude", "longitude"])
-        self.assertArrayEqual(r.data, np.array([1.0] * 6))
+        self.assertArrayAlmostEqual(r.data, np.array([1.0] * 6))
 
     def test_perfect_corr_all_dims(self):
         r = stats.pearsonr(self.cube_a, self.cube_a)
-        self.assertArrayEqual(r.data, np.array([1.0]))
+        self.assertArrayAlmostEqual(r.data, np.array([1.0]))
 
     def test_incompatible_cubes(self):
         with self.assertRaises(ValueError):
diff --git a/noxfile.py b/noxfile.py
deleted file mode 100755
index 601a1d576e..0000000000
--- a/noxfile.py
+++ /dev/null
@@ -1,301 +0,0 @@
-"""
-Perform test automation with nox.
-
-For further details, see https://nox.thea.codes/en/stable/#
-
-"""
-
-import hashlib
-import os
-from pathlib import Path
-
-import nox
-from nox.logger import logger
-
-#: Default to reusing any pre-existing nox environments.
-nox.options.reuse_existing_virtualenvs = True
-
-#: Python versions we can run sessions under
-_PY_VERSIONS_ALL = ["3.9", "3.10", "3.11"]
-_PY_VERSION_LATEST = _PY_VERSIONS_ALL[-1]
-
-#: One specific python version for docs builds
-_PY_VERSION_DOCSBUILD = _PY_VERSION_LATEST
-
-#: Cirrus-CI environment variable hook.
-PY_VER = os.environ.get("PY_VER", _PY_VERSIONS_ALL)
-
-#: Default cartopy cache directory.
-CARTOPY_CACHE_DIR = os.environ.get("HOME") / Path(".local/share/cartopy")
-
-# https://github.com/numpy/numpy/pull/19478
-# https://github.com/matplotlib/matplotlib/pull/22099
-#: Common session environment variables.
-ENV = dict(NPY_DISABLE_CPU_FEATURES="AVX512F,AVX512CD,AVX512_SKX")
-
-
-def session_lockfile(session: nox.sessions.Session) -> Path:
-    """Return the path of the session lockfile."""
-    return Path(
-        f"requirements/locks/py{session.python.replace('.', '')}-linux-64.lock"
-    )
-
-
-def session_cachefile(session: nox.sessions.Session) -> Path:
-    """Returns the path of the session lockfile cache."""
-    lockfile = session_lockfile(session)
-    tmp_dir = Path(session.create_tmp())
-    cache = tmp_dir / lockfile.name
-    return cache
-
-
-def venv_populated(session: nox.sessions.Session) -> bool:
-    """Returns True if the conda venv has been created
-    and the list of packages in the lockfile installed."""
-    return session_cachefile(session).is_file()
-
-
-def venv_changed(session: nox.sessions.Session) -> bool:
-    """Returns True if the installed session is different to that specified
-    in the lockfile."""
-    changed = False
-    cache = session_cachefile(session)
-    lockfile = session_lockfile(session)
-    if cache.is_file():
-        with open(lockfile, "rb") as fi:
-            expected = hashlib.sha256(fi.read()).hexdigest()
-        with open(cache, "r") as fi:
-            actual = fi.read()
-        changed = actual != expected
-    return changed
-
-
-def cache_venv(session: nox.sessions.Session) -> None:
-    """
-    Cache the nox session environment.
-
-    This consists of saving a hexdigest (sha256) of the associated
-    conda lock file.
-
-    Parameters
-    ----------
-    session: object
-        A `nox.sessions.Session` object.
-
-    """
-    lockfile = session_lockfile(session)
-    cache = session_cachefile(session)
-    with open(lockfile, "rb") as fi:
-        hexdigest = hashlib.sha256(fi.read()).hexdigest()
-    with open(cache, "w") as fout:
-        fout.write(hexdigest)
-
-
-def cache_cartopy(session: nox.sessions.Session) -> None:
-    """
-    Determine whether to cache the cartopy natural earth shapefiles.
-
-    Parameters
-    ----------
-    session: object
-        A `nox.sessions.Session` object.
-
-    """
-    if not CARTOPY_CACHE_DIR.is_dir():
-        session.run_always(
-            "python",
-            "-c",
-            "import cartopy; cartopy.io.shapereader.natural_earth()",
-        )
-
-
-def prepare_venv(session: nox.sessions.Session) -> None:
-    """
-    Create and cache the nox session conda environment, and additionally
-    provide conda environment package details and info.
-
-    Note that, iris is installed into the environment using pip.
-
-    Parameters
-    ----------
-    session: object
-        A `nox.sessions.Session` object.
-
-    Notes
-    -----
-    See
-      - https://github.com/theacodes/nox/issues/346
-      - https://github.com/theacodes/nox/issues/260
-
-    """
-    lockfile = session_lockfile(session)
-    venv_dir = session.virtualenv.location_name
-
-    if not venv_populated(session):
-        # environment has been created but packages not yet installed
-        # populate the environment from the lockfile
-        logger.debug(f"Populating conda env at {venv_dir}")
-        session.conda_install("--file", str(lockfile))
-        cache_venv(session)
-
-    elif venv_changed(session):
-        # destroy the environment and rebuild it
-        logger.debug(f"Lockfile changed. Re-creating conda env at {venv_dir}")
-        _re_orig = session.virtualenv.reuse_existing
-        session.virtualenv.reuse_existing = False
-        session.virtualenv.create()
-        session.conda_install("--file", str(lockfile))
-        session.virtualenv.reuse_existing = _re_orig
-        cache_venv(session)
-
-    logger.debug(f"Environment {venv_dir} is up to date")
-
-    cache_cartopy(session)
-
-    # Determine whether verbose diagnostics have been requested
-    # from the command line.
-    verbose = "-v" in session.posargs or "--verbose" in session.posargs
-
-    if verbose:
-        session.run_always("conda", "info")
-        session.run_always("conda", "list", f"--prefix={venv_dir}")
-        session.run_always(
-            "conda",
-            "list",
-            f"--prefix={venv_dir}",
-            "--explicit",
-        )
-
-
-@nox.session(python=PY_VER, venv_backend="conda")
-def tests(session: nox.sessions.Session):
-    """
-    Perform iris system, integration and unit tests.
-
-    Coverage testing is enabled if the "--coverage" or "-c" flag is used.
-
-    Parameters
-    ----------
-    session: object
-        A `nox.sessions.Session` object.
-
-    """
-    prepare_venv(session)
-    session.install("--no-deps", "--editable", ".")
-    session.env.update(ENV)
-    run_args = [
-        "pytest",
-        "-n",
-        "auto",
-        "lib/iris/tests",
-    ]
-    if "-c" in session.posargs or "--coverage" in session.posargs:
-        run_args[-1:-1] = ["--cov=lib/iris", "--cov-report=xml"]
-    session.run(*run_args)
-
-
-@nox.session(python=_PY_VERSION_DOCSBUILD, venv_backend="conda")
-def doctest(session: nox.sessions.Session):
-    """
-    Perform iris doctests and gallery.
-
-    Parameters
-    ----------
-    session: object
-        A `nox.sessions.Session` object.
-
-    """
-    prepare_venv(session)
-    session.install("--no-deps", "--editable", ".")
-    session.env.update(ENV)
-    session.cd("docs")
-    session.run(
-        "make",
-        "clean",
-        "html",
-        external=True,
-    )
-    session.run(
-        "make",
-        "doctest",
-        external=True,
-    )
-
-
-@nox.session(python=_PY_VERSION_DOCSBUILD, venv_backend="conda")
-def gallery(session: nox.sessions.Session):
-    """
-    Perform iris gallery doc-tests.
-
-    Parameters
-    ----------
-    session: object
-        A `nox.sessions.Session` object.
-
-    """
-    prepare_venv(session)
-    session.install("--no-deps", "--editable", ".")
-    session.env.update(ENV)
-    session.run(
-        "pytest",
-        "-n",
-        "auto",
-        "docs/gallery_tests",
-    )
-
-
-@nox.session(python=_PY_VERSION_DOCSBUILD, venv_backend="conda")
-def linkcheck(session: nox.sessions.Session):
-    """
-    Perform iris doc link check.
-
-    Parameters
-    ----------
-    session: object
-        A `nox.sessions.Session` object.
-
-    """
-    prepare_venv(session)
-    session.install("--no-deps", "--editable", ".")
-    session.cd("docs")
-    session.run(
-        "make",
-        "clean",
-        "html",
-        external=True,
-    )
-    session.run(
-        "make",
-        "linkcheck",
-        external=True,
-    )
-
-
-@nox.session(python=PY_VER, venv_backend="conda")
-def wheel(session: nox.sessions.Session):
-    """
-    Perform iris local wheel install and import test.
-
-    Parameters
-    ----------
-    session: object
-        A `nox.sessions.Session` object.
-
-    """
-    prepare_venv(session)
-    session.cd("dist")
-    fname = list(Path(".").glob("scitools_iris-*.whl"))
-    if len(fname) == 0:
-        raise ValueError("Cannot find wheel to install.")
-    if len(fname) > 1:
-        emsg = (
-            f"Expected to find 1 wheel to install, found {len(fname)} instead."
-        )
-        raise ValueError(emsg)
-    session.install(fname[0].name)
-    session.run(
-        "python",
-        "-c",
-        "import iris; print(f'{iris.__version__=}')",
-        external=True,
-    )
diff --git a/tools/update_lockfiles.py b/tools/update_lockfiles.py
index 073f86cda6..990bf5bcc7 100755
--- a/tools/update_lockfiles.py
+++ b/tools/update_lockfiles.py
@@ -5,7 +5,7 @@
 # licensing details.
 """
 A command line utility for generating conda-lock files for the environments
-that nox uses for testing each different supported version of python.
+that tox uses for testing each different supported version of python.
 Typical usage:
 
     python tools/update_lockfiles.py -o requirements/locks requirements/py*.yml
diff --git a/tox.ini b/tox.ini
new file mode 100644
index 0000000000..47a3204a25
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,40 @@
+[tox]
+requires =
+    tox-conda
+
+[testenv]
+conda_spec =
+    py39: {toxinidir}{/}requirements{/}locks{/}py39-linux-64.lock
+    py310: {toxinidir}{/}requirements{/}locks{/}py310-linux-64.lock
+    py311: {toxinidir}{/}requirements{/}locks{/}py311-linux-64.lock
+usedevelop =
+    true
+
+[testenv:py{39,310,311}-tests]
+description = Perform Iris unit, integration and system tests.
+commands =
+    pytest -n auto {posargs} {toxinidir}{/}lib{/}iris{/}tests
+
+[testenv:py{39,310,311}-gallery_tests]
+description = Perform Iris gallery tests.
+commands =
+    pytest -n auto {posargs} docs/gallery_tests
+
+[testenv:py{39,310,311}-docs{,-linkcheck,-tests}]
+description = Build, and optionally linkcheck or test, the Iris documentation
+allowlist_externals =
+    make
+changedir =
+    {toxinidir}{/}docs
+commands =
+    make clean html
+    linkcheck: make linkcheck
+    tests: make doctest
+
+[testenv:py{39,310,311}-wheel]
+description = Install wheel and test the Iris import
+skip_install = true
+deps =
+    {toxinidir}{/}dist{/}scitools_iris*.whl
+commands =
+    python -c "import iris; print(f'\{iris.__version__=\}')"