The fundamental foundations of professional competencies necessary for the in-depth study of high-tech electrical, electronic, communication devices and productive professional activities in the fields where they are applied are outlined. The basic concepts and laws of the theory of electrical circuits, methods of describing signals, methods of analyzing processes in circuits are explained and discussed in detail. The tendency towards a compact presentation of precisely basic information has been consistently maintained. At the end of each chapter of the textbook, control questions and tasks are collected.