I found some information about this on Scott Hanselmans Blog Does anybody exactly know what this mean? Is this only for the Office Primary Interop Assemblies, or can I also use this to Embed my Redemption library or other COM libraries? The process described in Scott Hanselman's blog is called Type Equivalence , a rather nebulous term for the CLR 4.0's support for COM interop type assemblies. Although I haven't had a chance to look at it, there is a video here at Channel 9 that discusses it: Raja Krishnaswamy and Vance Morrison: CLR 4 - Inside Type Equivalence http://channel9.msdn.com/shows