diff --git a/README.md b/README.md
index 4e136d1f081..4ba6e80c655 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,9 @@
+**This is Terria's fork of the Cesium repository. Changes should be made against the `terriajs` branch, and not `master`. Before submitting a pull request against this repository, please consider if your changes would be better made upstream in Cesium.**
+
+You can find our main repository, along with futher instructors for contributors at https://github.com/TerriaJS/terriajs.
+
+Cesium's README continues below.
+
 <p align="center">
 <img src="https://github.com/AnalyticalGraphicsInc/cesium/wiki/logos/Cesium_Logo_Color.jpg" width="50%" />
 </p>