Programming languages that conform to the CLI have access to the same base class library and are capable of being compiled into the same intermediate language (IL) and metadata. IL is then further compiled into native code particular to a specific architecture.

Because of this intermediate step, applications do not have to be rewritten from scratch. Their IL only needs to be further compiled into a system's native code.

Standard ECMA-335: CLI
This Standard defines the CLI.

Technical Overview of the Common Language Runtime
Microsoft document that describes the technical details of the CLI and compares them to the Java Virtual Machine.

The Joy of Rotor
Microsoft has released "Rotor," their shared-source version of the .NET Framework. The good, the bad, and the ugly of this million+ lines of code.