This chapter is devoted to several subsystem that are essential to the operation of accelerators. The first section deals with the control system and after giving a general overview of the architecture, the integration of devices is illustrated with the addition of an Arduino to an EPICS system. Particle sources for electrons, protons, and ions are the subject of the next section, followed by sections on injection methods and on beam cooling. The topic of the following section is the vacuum system, where both the hardware and computational methods are discussed. The final sections cover cryogenic systems and radiation protection issues.