The paper describes some of the problems which arise in providing for security of supplies and economical operation on the British Grid system. Under these two headings separate consideration is given to long-term and short-term planning.Long-term planning of the system determines what generating plant and transmission equipment will be provided, and the paper indicates the extent to which actual plant/load conditions have varied from those which were planned three years previously.Short-term planning is concerned with the operation of the system as it exists and a description is given of a typical day's operation of the British Grid system. Reference is also made to the operation of the system during the 1947 fuel crisis and to other operating conditions of special interest.Probable future developments associated with load dispatching are mentioned and special attention is drawn to the financial savings which could be obtained by providing better availability on high-merit plant.