In computer science, computer engineering, and telecommunications, a network is a group of communicating computers known as hosts, which communicate data to other hosts via communication protocols, as facilitated by networking hardware.

Within a computer network, computers are identified by network addresses, which allow rule-based systems such as Internet Protocol to locate and identify hosts. Hosts may also have hostnames, memorable labels for the host nodes, which are rarely changed after initial assignment. The physical medium that supports information exchange includes wired media like copper cables, optical fibers, and wireless radio-frequency media. The arrangement of hosts and hardware within a network architecture is known as the network topology.

The first computer network was created in 1940 when George Stibitz connected a terminal at Dartmouth to his Complex Number Calculator at Bell Labs in New York. Today, almost all computers are connected to a computer network, such as the global Internet or embedded networks such as those found in many modern electronic devices. Many applications have only limited functionality unless they are connected to a network. Networks support applications and services, such as access to the World Wide Web, digital video and audio, application and storage servers, printers, and email and instant messaging applications.

Computer networks may be classified by many criteria, including signal transmission medium, bandwidth, communication protocols, network size, topology, traffic controls, and purpose.