The Common Language Specification (CLS)
we used the term ’.Net Compliant Language’ and stated that all the .Net compliant languages can make use of CLR and FCL. But what makes a language a
 ’.Net compliant’ language? The answer is the Common Language Specification (CLS). Microsoft has released a small set of specifications that each language should meet to qualify as a .Net Compliant Language. As IL is a very rich language, it is not necessary for a language to implement all the IL functionality; rather, it merely needs to meet a small subset of CLS to qualify as a .Net compliant language. This is the reason why so many languages (procedural and OO) are now running under the .Net umbrella.