The potential applications and practical implementation of state-estimation techniques in an electric power system are discussed. The state estimator is a digital information-processing scheme which constitutes the real-time data base from which many of the central control, monitoring, display, alarm, interrogation and logging functions derive their information. An efficient algorithm for on-line state estimation is introduced, and the experimental results obtained on a 400-node network example are presented. A promising method for network reduction is proposed to take into account the effects of interconnected neighboring systems. Input data requirements of the power system control and dispatch functions are investigated, and the preliminary computational requirements are discussed. The present knowledge in power system state estimation is summarized, and areas of future development are defined.