This chapter describes and classifies electrical machines as well the values of sinusoidal alternating current. In addition, it presents the magnetization curve of ferromagnetic materials as well as the hysteresis cycle. This chapter provides some examples for illustrating the electromagnetic laws to ferromagnetic materials and applies the basic laws to magnetic circuits. It also reviews the magnetic quantities and units as an example of magnetic field generation in electromagnets. It finishes with an analysis of how an electric machine works.