The Composite Application Guidance for WPF and Silverlight is designed to help you more easily build enterprise-level Windows Presentation Foundation (WPF) client applications. This guidance will help you design and build flexible composite client applications-composite applications use loosely coupled, independently evolvable pieces that work together in the overall application.
The Composite Application Guidance can help you develop your client application in a modular fashion. With this approach, you manage the complexity of a large application by breaking it down into smaller, simpler modules. The modules can evolve independently while working together as a unified application.
This version of the Composite Application Guidance is designed to help you build applications in WPF and Silverlight that have a single code base.
The guidance includes a reference implementation, reusable library code (named the Composite Application Library), documentation, QuickStarts, and hands-on labs.
http://msdn.microsoft.com/en-us/library/dd458809.aspx