The first computers were stand-alone machines that one person used at a time. Later, timesharing computers were invented that allowed more than one person to use the machine concurrently. When personal computers (PCs) came along, the one computer–one user paradigm came back with a vengeance. But all that is in the past. Today, most computers are networked, i.e., connected to one another so that they can communicate with one another, share resources, and access the Internet. Virtually 100 percent of business and industrial computers are networked. It is estimated that more than 70 percent of all home and personal computers are also networked. This chapter is an introduction to networking and local-area networks (LANs).