diff --git a/Settings.md b/Settings.md
index 5f5d9d2..1b921ea 100644
--- a/Settings.md
+++ b/Settings.md
@@ -1,3 +1,15 @@
-Deployment type settings should go in override modules e.g `app/polyphonic/settings/dev.py`.
+## Environment
 
-Instance variables like `SECRET_KEY` and `WORK_DIR` should be set in the environment.
\ No newline at end of file
+The following can be modified on a per-instance basis by setting the environment:
+
+* `SECRET_KEY` - Should be unique (required)
+* `WORK_DIR` - Where to store DB, index and cached files (defaults to `BASE_DIR/data`)
+* `DEBUG` - enable debug output
+
+## Settings files
+
+These all derive from `polyphonic.config.settings.base`
+
+* `base` - some sensible defaults.
+* `dev` - enables logging and the debug toolbar
+* `docker` -  adds the WhiteNoise module. Should remove this as docker packing adds a custom settings file.