The .NET Framework
The .NET Framework is a high-productivity, standards-based, multilanguage application execution environment. It consists of a runtime environment called the common language runtime and a set of libraries to boost programmers' productivity.
Common Language Runtime
The common language runtime, or just the runtime, is Microsoft's implementation of the ECMA CLI specification. When a .NET application is run, the common language runtime manages the loading and execution of the code and provides many runtime services to the application.
If you have been developing your code under COM, you will be surprised by the simplicity the .NET model offers. Forget dealing with GUIDs, CLSIDs, PROGIDs, IDL, type-libraries, apartments, server registration, ...