XAML (Extensible Application Markup Language) is an xml based language for creating trees of .NET objects. It is being used not only in Windows Presentation Foundation (WPF) but also in Windows Workflow Foundation (WF). The strenght behind this language is it’s human readable and writeable. This channel 9 video There's Something About XAML presented by Rob Relyea a Program Manager on the WPF team talks about the history of XAML, how it's been designed, how it works, what a BAML file is and what's in it, how the build process works, thoughts on debugging, tooling, and much more. This is a really cool video with lots of great content.