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+## Cross-domain iFrame Automation
+
+[Same-origin policy](https://en.wikipedia.org/wiki/Same-origin_policy) prevents Appium from automating iFrames that have a different domain to the parent.
+
+### Subdomain workaround
+If the parent and the iFrame share the same domain (e.g. `site.com` and `shop.site.com`), you can
+set `document.domain` on both the parent and each iFrame to a common domain. This solves the same-origin policy issue and allows automation. For example:
+
+Parent:
+```
+<html>
+  <head>
+    <script>
+      document.domain = 'site.com';
+    </script>
+  </head>
+  <body>
+    <iframe src="http://shop.site.com" width="200" height="200"></iframe>
+  </body>
+</html>
+```
+
+Child iFrame:
+```
+<html>
+  <head>
+    <script>
+      document.domain = 'site.com';
+    </script>
+  </head>
+  <body>
+    <p>This is an iFrame!</p>
+  </body>
+</html>
+```
