This monograph is an in-depth analytical review of automatic control systems and devices, focusing on the principle of operation underlying them. In the modern world, automatic regulation plays a key role in ensuring stability and optimizing the functioning of a variety of technical and technological systems. The purpose of this monograph is to summarize and systematize the knowledge about the principles of operation of automatic control systems, their influence on the performance and reliability of systems, as well as the latest trends in the development and application of such systems.