“Silverlight class library” Vs “Windows class library” Figure1: Silverlight library
Figure2: Normal library
1. It is not possible to reference from a Silverlight assembly to a regular .NET assembly but it is possible to do so the other way round. It is because the Silverlight CLR is a subset of .Net CLR. Every class and methods that Silverlight CLR has .Net CLR also have, but the other way round is not true. There are assemblies in .Net Framework that cannot be processed by Silverlight browser plug-in. 2. Silverlight class library template is differente than the Windows class library template. It is because Silverlight CLR is different is different that .Net CLR 3. It is not possible to choose the .Net Framework version in Silverlight class library. (VS2008)
Reference: http://www.devx.com/RIA/Article/40074