At the most basic level it provides the underlying implementation of all the fundamental types, including the numeric types, string, enum, delegate, and array.

At a second level it serves as a system class library, providing support for input/output, collection classes, exceptions, regular expressions, sockets, threads, Web requests, and so on.

At a third level it provides a framework for complex application domains, such as Windows Forms (Chapter 6), Web Forms (Chapter 7), eXtensible Markup Language (XML), and the tabular display of data, often retrieved from a database.