The .NET Framework 4 works side by side with the Framework version 3.5 SP1. Applications that are based on earlier versions of the Framework will continue to run on that version. Just a subset of functionality is shared by all versions of the Framework.
Innovations in the Visual Basic and C# languages, for example statement lambdas, implicit line continuations, dynamic dispatch, and named/optional parameters.

- The ADO.NET Entity Framework, which simplifies how developers program against relational databases by raising the level of abstraction, has many new features. These includes persistence ignorance and POCO support, lazy loading, test-driven development support, functions in model, and new LINQ operators.

- Enhancements to ASP.NET:
New JavaScript UI Templates and databinding capabilities for AJAX.
New ASP.NET chart control.