This book is written on the basis of the authors' achievements in teaching and research over many years in the field of ac machines and systems at Tsinghua University, and reflects the new developments in and applications of science and technology in recent years. When researching on the systems related to ac machines as main roles, analysis methods and operating performance are stressed in this book. This book is divided into six chapters. Chapter 1 makes salient-pole electric machines as the main subject of study. Considering ac machine as a circuit model composed of stator and rotor having relative motion, and starting from a single coil, the mathematic models and parameter calculation methods are discussed. Chapter 2 discusses electromagnetic relations and parameters of synchronous machines and their several operating conditions at synchronous speed, such as 3-phase sudden short circuit, sudden increase of load, opening short circuit, etc. Chapter 3 introduces some special operating modes of synchronous machine systems at constant speed and variable speed, such as two phase sudden short circuit, asynchronous operation of synchronous machines, asynchronous starting of synchronous motors, synchronous machine in connection with capacitances, cycloconverter-fed synchronous motor, ac-dc hybrid loads of synchronous machines, etc. Chapter 4 analyses oscillation, stability and excitation regulation of synchronous machine systems. Chapter 5 introduces electromagnetic relations of induction machines, some of their operating modes, such as starting characteristics, reswitching process, self-excitation during motor in series with capacitances, and combination system for polyphase induction generator with dual windings and rectified load. Chapter 6 provides description of inner asymmetric problems in the stator winding and squirrel-cage rotor of ac machines. This book is a textbook for the postgraduates in the field of electric machines and control, and also a reference book for technicists as well as for the teachers and students of relevant specialties in universities and colleges.