Electric motors are machines that help us to transform electrical energy into mechanical energy or, in other words, into motion. These machines can be found in our daily lives in devices ranging from small household appliances to large-capacity motors in industry. Electric motors have become popular over the last few decades owing to their use in driving vehicles for transporting people or even heavy loads. In fact, today, they have become very popular in transportation vehicles that use alternative energy sources for their operation, and electric power is one of the most promising. Although electric motors are very popular in various applications, the principle of operation of an electric motor has rarely been questioned. In this chapter, we will focus on how its main components, such as permanent magnets, winding, and core, through physical or more specifically electromagnetic properties, can create magnetic fields that will be used to generate motion. Therefore, concepts such as the magnetic field, magnetic flux density, magnetic forces, electromagnetic induction, and Ampere’s and Faraday's law are presented. In addition, the electromagnetic principles that allow the conversion of electrical energy into motion by means of an electric motor are explained, as well as its components. We will focus on the analysis of magnetic circuits, which are magnetic circuits with a metallic structure that can be wound by means of a conductor where its current will produce a magnetic flux or the use of permanent magnets, because they can maintain the state of magnetization without the need for external energy. In addition, the calculation of the magnetic flux density, fundamental elements of an electromagnet such as the core, coils, and air spaces, as well as the hysteresis and magnetic saturation properties, are discussed.