Microsoft Intermediate Language (MSIL):

Specification for a platform independent, low-level, stack-based assembly-like language

Common Language Runtime (CLR):

A common runtime for all .NET applications, compiles and executes MSIL

Class libraries:

Common functionality that can be used by all languages

Includes Windows Forms for GUI development

Language compilers:

C#, C++, VB…

Distributed computing:

Networking using sockets, Remoting, Web Services and Applications using ASP.NET