F# is a succinct, expressive, and efficient functional and object-oriented language for .NET
F# is a succinct, expressive, and efficient functional and object-oriented language for .NET, which helps you write simple code to solve complex problems. It is a descendant from the ML family of programming languages.
For more information about F#, visit the F# homepage at MSDN.
See also Getting Started with F# for lots more information, including links to blogs, videos, books, "hello world"s, downloads, and more.
For tips and tricks on transitioning to functional languages (especially F#) there is also F# For Fun and Profit.