This book comprehends basic and advanced theoretical tools for the analysis of structure and operation of power electrical machines. The principal machine typologies are discussed: single and three phase transformer, induction machine, and synchronous machine. The first chapter resumes important notions of electromagnetism, oriented to the study of electrical machines: starting from the properties of Maxwell’s equations in matter (in particular in magnetic materials), electric and magnetic integral laws and their application to practical electric and magnetic circuits are explained. In the subsequent chapters the electrical machines are analyzed in first from a physical point of view, and then suitable models, equations, and equivalent circuits are derived from the fundamental principles. The AC operation is deepened, by using both time-domain and frequency domain equations and equivalent circuits, since this is the main operating modality. The text is mainly targeted to students enrolled in a Master degree in Electrical Engineering, and is designed to be used for a one- or two-semester course in electrical machines. The prerequisites for effective use of the text are the courses of mathematical analysis, physics, and circuit theory.