Prism provides guidance in the form of samples and documentation that help you easily design and build rich, flexible, and easily maintained Windows Presentation Foundation (WPF) desktop applications. Using design patterns that embody important architectural design principles, such as separation of concerns and loose coupling, Prism helps you to design and build applications using loosely coupled components that can evolve independently but that can be easily and seamlessly integrated into the overall application. In short, these applications are "built to last" and "built for change." These types of applications are known as composite applications.
What’s new for Prism 5.0 for WPF?
When we first created Prism one of the primary goals was to allow developers to use the components that they needed for their applications. For this release we took it a step farther by separating the features into separate assemblies – Prism.Composition, Prism.Mvvm (portable class library), Prism.PubSubEvents (portable class library), and Prism.Interactivity.