This book is an extension and refinement of the lectures delivered by the authors in the Moscow Power Institute for students speciali¬zing in Automation and Remote Control, Computer Engineering, information and measurement technology, Electric Drives and Automation of Industrial Facilities.It is a textbook on Automatic Control Theory written to imple¬ment a program approved by the Ministry of Higher and Secondary Specialized Education of the USSR.The selection and presentation of the material was greatly influen¬ced by lectures delivered by Professors L. S. Goldfarb and Ya. Z. Tsypkin in the Moscow Power Institute over many years. The subject matter of some of Goldfarb's lectures is included in the hook.The sequence of presentation is the result of studying the logical relations between the various parts of the curriculum. In this book the material is presented so as to minimize the time gaps between logically related parts of the curriculum.