Somasegar: Visual Basic, C# More Interoperable with Python, JScript, and Other Dynamic Languages
C# 4.0's major themes are interoperability with dynamic programming paradigms and improved Office programmability. Dynamic lookup, a new feature in C# 4.0, allows you to use and manipulate an object from IronPython, IronRuby, JScript, the HTML DOM, or a standard .Net library in the same way, no matter where it came from.
This allows dynamic languages to expose their objects to C# in a way that feels natural to a C# programmer.