The .NET Framework is Microsoft's comprehensive and consistent programming model for building applications that have visually stunning user experiences, seamless and secure communication, and the ability to model a range of business processes.
The .NET Framework 4 works side by side with older Framework versions. Applications that are based on earlier versions of the Framework will continue to run on the version targeted by default.
The Microsoft .NET Framework 4 includes the following new features and improvements:
Improvements in Common Language Runtime (CLR) and Base Class Library (BCL).
Innovations in the Visual Basic and C# languages, for example statement lambdas, implicit line continuations, dynamic dispatch, and named/optional parameters.
Improvements in Data Access and Modeling.
Enhancements to ASP.NET.
Improvements in Windows Presentation Foundation (WPF).
Innovative new parallel-programming features such as parallel loop support, Task Parallel Library (TPL), Parallel LINQ (PLINQ), and coordination data structures which let developers harness the power of multi-core processors.