At my Houston MSDN Event (http://www.msdnevents.com) I had a student ask me if it was possible to do a Join between different data sources using LINQ. Specifically, he asked about joining XML data with SQL data. So I thought "What the hell, let's give it a shot." It turns out you CAN do joins between different data sources with no problems that I can see. Here is my example of how to join SQL and XML data using LINQ.