--- a/doc/crossdomain.md
+++ b/doc/crossdomain.md
@@ -1,1 +1,22 @@
+[HTML5 Boilerplate homepage](http://html5boilerplate.com) | [Documentation
+table of contents](README.md)
 
+# crossdomain.xml
+
+A cross-domain policy file is an XML document that grants a web client—such as
+Adobe Flash Player, Adobe Reader, etc., permission to handle data across
+multiple domains. When a client hosts content from a particular source domain
+and that content makes requests directed towards a domain other than its own,
+the remote domain would need to host a cross-domain policy file that grants
+access to the source domain, allowing the client to continue with the
+transaction. Policy files grant read access to data, permit a client to include
+custom headers in cross-domain requests, and are also used with sockets to
+grant permissions for socket-based connections.
+
+For full details, check out Adobe's article about the [cross-domain policy file
+specification](http://www.adobe.com/devnet/articles/crossdomain_policy_file_spec.html)
+
+Read the [Cross-domain policy file
+specification](http://learn.adobe.com/wiki/download/attachments/64389123/CrossDomain_PolicyFile_Specification.pdf?version=1)
+- (PDF, 129 KB)
+