diff --git a/README.md b/README.md
index c1020fd..87d80e4 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,9 @@
+# NOTE: THIS IS THE DEVELOPMENT BRANCH
+
+This document is the "master" branch, which is under active development.  If
+you are looking for docs on released versions of git-sync, you probably want to
+use the [v3.x branch](https://github.com/kubernetes/git-sync/tree/release-3.x).
+
 # git-sync
 
 git-sync is a simple command that pulls a git repository into a local directory.