Python compatibility

Since IronPython is a implementation of Python 2.7, any Python documentation is useful when using IronPython.

.NET Integration

IronPython's sweet-spot is being able to use the .NET framework APIs directly from Python.

Silverlight Integration

IronPython also runs in all major web-browsers through Silverlight, which contains a significantly large subset of the .NET framework APIs.

Books

IronPython in Action Cover

IronPython in Action by Michael Foord and Christian Muirhead, offers a comprehensive, hands-on introduction to Microsoft's exciting new approach for programming the .NET framework.

Source Code

When all else fails, you can always look at the IronPython source code

Implementation

Regression Tests - List of regression tests currently passing