Küpfmüller's standard work "Introduction to Theoretical Electrical Engineering" is now in its 20th edition. This textbook is distinguished by its unique didactics: the physical motivation takes precedence over a primarily mathematical treatment of the topics. All chapters have been standardized and organized more clearly, with the arrangement of topics adapted to current teaching practices. The justification of field-theoretical concepts is based on key experiments, from which approaches to approximation theories are developed all the way to the complete Maxwell equations. Modern symbolism and contemporary practical examples are included. Numerous worked-out application examples from electrical engineering are also available. Additionally, there are extras online: extensive didactic materials, further worked-out examples, and documents from the history of the work.