David Hill from the patterns & practices team posted a very interesting article concerning MEF and Prism. It talks about the benefits your applications get from using these extensibility technologies, but also clears some misunderstandings regarding their purpose. I’ve been faced with this question several times and the online community reflects this same common overlap. While MEF is purely an extensibility API, Prism is a development pattern that allows you to organize and manage your WPF/Silverlight project through modularity and thus isolate requirement and functionality concerns in development teams.

They’re both part of .NET Framework 4.0 and a MUST if you are developing big applications and/or needing your software to be extensible.

Check out the article here.