diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 3ecaeac..ed4281f 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -62,8 +62,7 @@ setup.py  # Project is pip-installable, project requirements managed here.
 
     * On a Mac, you can run `brew install miniconda`.
 
-    * Use Python version 3.8.5+ for development. We have not yet upgraded the project to use Python 3.9
-      (see [#166](https://github.com/google/weather-tools/issues/166)).
+    * Use Python version 3.8.5+ for development. 
 
 3. Clone the repo and install dependencies with anaconda.
 
diff --git a/tox.ini b/tox.ini
index ded13c4..2e71b30 100644
--- a/tox.ini
+++ b/tox.ini
@@ -13,7 +13,7 @@
 # limitations under the License.
 
 [tox]
-envlist = py37,py38,lint,type
+envlist = py38,py39,lint,type
 
 [testenv]
 deps = .[test]