The address reviews the planning of the original Grid system, and indicates the influence on system planning of the war years and the changes prior to nationalization. It then deals with the changed basis of planning since nationalization, and with the principal factors which have led to the present pattern of system planning and design. These include tariff changes, the changing design of generators and generating stations, the size and type of loads, and the standardization of transmission plant and equipment. Their effect is shown in examples from the North-Eastern Region of the Central Electricity Generating Board.