What is Common Language Specification (CLS)?
CLS is a set of essential rules, which must be followed by each .NET language to be a .NET- compliant language. It enables interoperability among two .NET-compliant languages. CLS is a subset of CTS; therefore, the languages supported by CLS can use each other's class libraries same to their own. Application programming interfaces (APIs), which are designed by following the rules explained in CLS can be used by all .NET-compliant languages.