The document discusses the Managed Extensibility Framework (MEF) and how it can be used to create extensible applications in .NET. MEF allows third parties to extend applications through imports and exports. It decouples internal application components and allows overriding built-in defaults. MEF is part of .NET 4.0 but can be used on .NET 3.5 through a Codeplex project. The document provides an agenda on MEF basics, extensibility in .NET 2.0 versus MEF, demos of MEF functionality, and resources for additional information.