A wide area network or WAN is a computer network covering a wide geographical area, involving vast array of computers. This is different from personal area networks (PANs), metropolitan area networks (MANs) or local area networks (LANs) that are usually limited to a room, building or campus. The best example of a WAN is the Internet.

WANs are used to connect local area networks together, so that users and computers in one location can communicate with users and computers in other locations. Many WANs are built for one particular organization and are private, others, built by Internet service providers provide connections from an organization's LAN to the Internet. WANs are most often built of leased lines. At each end of the leased line, a router connects to the LAN on one side and a hub within the WAN on the other. A number of network protocols may use the basic physical transport mechanism including TCP/IP. Other protocols including X.25, ATM and Frame relay can also be used for WANs.

Now that the Internet provides a high speed WAN, the need for a private network made up of leased lines owned by the organization which wants to connect the sites has decreased. Virtual private networks are often used instead. These use encryption and other techniques to make it appear that the organization has a dedicated network while making use of the shared infrastructure of the WAN.

Academic research into wide area networks can be broken down into three areas: Mathematical models, network emulation and network simulation.