diff --git a/README.md b/README.md
index 6dfd94ff..bca802ef 100644
--- a/README.md
+++ b/README.md
@@ -13,8 +13,14 @@
 
 ## Running (development)
 
+To start the app and watch for changes:
+
     DEBUG=1 ./app.py
 
+To rebuild css whenever the scss changes:
+
+    ./gen-css --watch
+
 ## Notes
 
 tornado templates are like mustache templates -- add the
diff --git a/gen-css b/gen-css
index da4cb20c..ad996c67 100755
--- a/gen-css
+++ b/gen-css
@@ -1,5 +1,14 @@
-#!/bin/sh -x
+#!/bin/sh
+
+opts=$1
 
 cp -a node_modules/uswds/dist/fonts static/
-sass scss/atat.scss > static/assets/atat.css
+
+if [ "$opts" == "--watch" ]; then
+    set -x
+    sass --watch scss/atat.scss:static/assets/atat.css
+else
+    set -x
+    sass scss/atat.scss > static/assets/atat.css
+fi