“With the release of .NET Framework 4, it’s relevant to talk about migration issues you might run into when upgrading your applications to .NET 4. My team has put together a topic that describes the migration issues (formerly known as breaking changes) between .NET Framework 3.5 Service Pack 1 and .NET Framework version 4. The change in terminology is to reflect the fact that not all changes introduced by a new version of the framework break your application; rather, these are changes in behavior discovered during design review and testing that could potentially impact an application,” Maira Wenzel explained. We’ll update our portal (.NET Framework Version and Assembly Information) that points to different migration issues topics to include .NET 4 version as well. So in a nutshell, these’re migration issues topics we’ve published so far and their locations: .NET Framework 4 Migration Issues (from .NET 3.5 SP1 to .NET 4), .NET Framework 3.5 SP1 Migration Issues (from .NET 3.5 to .NET 3.5 SP1), .NET Framework 2.0 Migration Issues (from .NET 1.0/1.1 to .NET 2.0).