The BCL (Base Class Library) is a combination of classes or we can say that it’s a Library of functionalities and types available to all languages that used in .NET Framework. To make the programmer job more easier dot net gave a advantage to includes the BCL in order to collect a large number of common functions, just like to read a file and write to file, graphic rendering, database interaction, and XML document manipulation at one place . The scope of this is large and Standard Libraries for most other languages, including C++, and would be comparable in scope to the standard libraries is just like Java. The BCL is sometimes incorrectly referred to as the Framework Class Library (FCL), which is a superset including the Microsoft namespaces.