There are numerous potential benefits associated with electrified aircraft propulsion (EAP). Achieving economical and safe EAP in transport aircraft would constitute an enormous leap forward in aviation. However, as with all potential engineering breakthroughs, the devil is in the details. This chapter begins to examine some of these details by introducing the electric power system (EPS) and summarizing its design, control, and protection functions. With the electrification of propulsion systems, EPS power levels (i.e., generation, distribution, and loads) are expected to increase by at least an order of magnitude, with far-reaching implications on the overall system design. Since all aspects of the EPS will be impacted, a thorough understanding and appreciation of the EPS and its functions is necessary to fully comprehend the challenges ahead. Several key EPS components and functions are described, and the solid foundation provided by the material in this chapter prepares the reader for the focused discussions of individual system components that follow in subsequent chapters.