A messaging service is one of the most effective and popular mediums to communicate between two machines. It doesn't matter if you're a high-tech developer, a stockbroker, a high-school student, or a businessperson. In some means, you probably use messaging services. Some of the common messaging services are electronic mail (email), instant messenger services, text messaging via phones, or messaging used in complex distributed applications. This chapter covers messaging and its related functionality defined in the .NET Framework Class Library, as well as how to use it in your applications.