It was a simple enough question that Ethan, my .NET remoting student, asked me yesterday. I did some research, and couldn't find anything official from Microsoft, just their human readable schema on MSDN. Then I found radsoftware's page, which offers a product providing Intellisense to your VS.NET 1.X config file editor. About half way down the page is a ZIP file containing an XSD schema that they built. It looks pretty thorough, but I sent off an email just to make sure.