This article is a tutorial on local area networks (LAN) for radiology applications. LANs are being implemented in radiology departments for the management of text and images, replacing the inflexible point-to-point wiring between two devices (computer-to-terminal). These networks enable the sharing of computers and computer devices, reduce equipment costs, and provide improved reliability. Any LAN must include items from the following four categories: transmission medium, topology, data transmission mode, and access protocol. Media for local area networks are twisted pair, coaxial, and optical fiber cables. The topology of these networks include the star, ring, bus, tree, and circuit-switching. Data transmission modes are either analog signals or digital signals. Access protocol methods include the broadcast bus system and the ring system. A performance measurement for a LAN is the throughput rate as a function of the number of active computer nodes. Standards for LANs help to ensure that products purchased from multiple manufacturers will operate successfully.