Modern applications are often built from pluggable parts composed together either at development time or at runtime. Such parts might include reusable libraries, application add-ins, host provided services, or internal parts separated from the main application for engineering reasons; The .NET framework currently provides basic functionality for loading such parts, but it does not provide a built-in mechanism for discovering and composing them. The Managed Extensibility Framework (MEF) is a new .NET Framework technology designed to enable development of parts and applications composed from such parts. This session will cover the basic MEF usage scenarios and architecture.