After a brief account of the reasons for introducing computers into power stations, the extent of the applications of computers in the UK and abroad and the economic factors involved are discussed. The differing conditions for nuclear and thermal stations are identified. These lead to different reliability specifications and scopes of requirements. The role of the computer in alarm and data display, logging and control is outlined, and the available hardware and software techniques are reviewed, with special reference to cathode-ray-tube displays for alarms and data, the latter being in the form of alphanumeric tables, graphs or pictorial representations. The systems engineering and planning of projects are considered in relation to the specifications of hardware and software and their production, system testing and installation at the site. The relationship of these activities to the main power-station-erection programme is summarised. A method of specifying the system reliability is given, and the requirements are interpreted in terms of the system configuration with the use of redundancy. Schemes employing multiple central processor units and interconnecting highways are described, and some availability figures are reported for systems in service. The safety implications of using computers and the problems of operator-computer communication are summarised. Details are tabulated of the duties and hardware of some UK power-station computer systems, and an indication is given of the directions that may be taken by future developments.