Electric power systems represent an important aspect of energy development policy. Within this context, the study of these systems through their simulation affords one of the best methods of ensuring optimal development and operation. For many years, electricity companies and manufacturers have been simulating electric power systems. Many changes have occurred, associated with the introduction of new equipment and the technical progress which, in particular, made it possible to model electrical engineering equipment thanks to the use of electronic components. The changeover to the fully digital approach, made possible by rapid advances in computing power, constitutes a challenge for the 1990s and several such systems have already been constructed throughout the world. This approach offers numerous advantages, both economic and technical, greater ease of use, better upgradability and the reproducible nature of the simulations. The authors provide a comprehensive treatment of the modelling and simulation techniques currently in use. The text emphasizes model design applied to power plants producing energy, generators and motors carrying out energy transformations and networks transmitting energy. The systems are analyzed considering each process, from steady state to fast transients, with detailed explanation of the problem to be solved, the choice of models and methods for optimising efficiency. Many examples and references are provided. The book is intended for anyone involved in power system engineering, from practising design and development engineers to researchers and postgraduate and advanced undergraduate students.