.NET Framework 3.5 builds upon version 2.0 and 3.0

The .NET Framework 3.5 builds upon version 2.0 and 3.0 of the .NET Framework, so it essentially contains the following components:

.NET Framework 2.0 and .NET Framework 2.0 Service Pack 1
.NET Framework 3.0 and .NET Framework 3.0 Service Pack 1
New features in .NET 3.5