This document discusses the Microsoft Biology Foundation (MBF), an open source bioinformatics toolkit built on the .NET Framework. MBF provides components for working with biological data formats, sequences, and algorithms. It is intended as a foundation for other tools and applications to build upon, rather than an application itself. The community around MBF consists of scientific programmers with a range of expertise. MBF is cross-platform, with new features in version 2 including advanced math functions, comparative assembly, command line tools, and visualization capabilities. The source code and community are hosted on Codeplex to encourage open source development of the toolkit.