using pre .net 4.0 projects or libraries within a .net 4.0 library?

Is it permissible? that is, for example, using a .net 2.0 library within a .net 4.0 project, or having a .net 2.0 project side-by-side a .net 4.0开发者_开发知识库 project within the same solution interacting with each other?

I am using Visual Studio 2010

Thank you

Yes, it's permissible.

.NET 4 assemblies will reference and use .NET 2/3.5 assemblies with no issues.

However, you can't reference a .NET 4 library from a CLR 2 (.NET 2.0/3.5) project.