The Managed Extensibility Framework (MEF) is a new library in .NET that enables greater reuse of applications and components. Using MEF, .NET applications can make the shift from being statically compiled to dynamically composed. If you are building extensible applications, extensible frameworks and application extensions, then MEF is for you.

MEF Contrib is a community-developed library of extensions to the Managed Extensibility Framework (MEF), a new library in .NET.

MEF 101