diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..af0aace
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,16 @@
+# Release 20.09 (unreleased)
+
+## State version changes:
+
+These changes are only active
+if the `system.stateVersion` option is set to `"20.09"` or later.
+
+* `home-manager.useUserPackages` now defaults to `true`.
+  The developers are not aware of any adverse effects so far.
+
+## Other compatibility considerations:
+
+* Pre-module-system installations are not supported anymore with this release.
+  If you are not on `release-19.09` yet,
+  either or attempt an upgrade to `release-19.09`
+  and follow the instructions, or backup and reinstall (preferred).