In this chapter, we introduce some of the basic networking concepts and protocols. The chapter serves as a foundation to networking that will allow you to tackle programming in the rest of the book. It doesn’t matter if you plan to develop server applications running as Windows Services (offering some data for clients using a custom protocol), if you write client applications that request data from web servers, or if you create multicasting or mailing applications—you should start with reading this chapter. If you don’t already know what a router or a network switch is, if you aren’t sure about the functionality of the seven layers in the Open Systems Interconnection (OSI) protocol model, or if you just want a refresher or an overview of the different network protocols and their uses, then this chapter is addressed to you.