A primary interop assembly is a unique, vendor-supplied assembly that contains type definitions (as metadata) of types implemented with COM. There can be only one primary interop assembly, which must be signed with a strong name by the publisher of the COM type library. A single primary interop assembly can wrap more than one version of the same type library.

A COM type library that is imported as an assembly and signed by someone other than the publisher of the original type library cannot be a primary interop assembly. Only the publisher of a type library can produce a true primary interop assembly, which becomes the unit of official type definitions for interoperating with the underlying COM types.

Publishers of COM components produce primary interop assemblies and distribute them to developers for use in .NET Framework applications. For publishers, this section provides information about producing primary interop assemblies. For developers, this section describes how to program with primary interop assemblies.