WHAT : is .NET Common Language Runtime (CLR) Framework The Common Language Runtime (CLR) is a an Execution Environment . Common Language Runtime (CLR)'s main tasks are to convert the .NET Managed Code to native code, manage running code like a Virtual Machine, and also controls the interaction with the Operating System. As part of Microsoft's .NET Framework, the Common Language Runtime (CLR) is managing the execution of programs written in any of several supported languages. Allowing t