The CLI (Common Language Infrastructure) is the definition of the fundamentals ofthe .NET framework – the Common Type System (CTS), metadata, the Virtual
Execution Environment (VES) and its use of intermediate language (IL), and the
support of multiple programming languages via the Common Language Specification
(CLS). The CLI is documented through ECMA – see
http://msdn.microsoft.com/net/ecma/ for more details.
The CLR (Common Language Runtime) is Microsoft’s primary implementation of the
CLI. Microsoft also have a shared source implementation known as ROTOR, for
educational purposes, as well as the .NET Compact Framework for mobile devices.
Non-Microsoft CLI implementations include Mono and DotGNU Portable. NET.