The first volume of the textbook gives the physical foundations of electrical engineering and electronics, examines the properties of electrical signals, outlines the theory of linear and nonlinear electrical circuits with sources of direct and sinusoidal current in steady and transient modes. At the same time, special attention is paid to physical processes and phenomena, in particular energy ones, as initiators of the distribution of currents in circuit elements. A systematic approach is used when presenting material, when objects of study - processes and devices are represented by hierarchical physical and mathematical models.