Off-grid systems make use of a variety of converters and controllers to condition and facilitate the flow of power from source to load. This chapter begins with an introduction to the fundamentals of power electronics that are important to understanding converters and controllers: solid-state switches and pulse width modulation. The operating principles, applications, and practical considerations of several DC converters and rectifiers are presented, including DC–DC converters, maximum power point trackers, charge and diversion load controllers, single- and three-phase rectifiers, and automatic voltage regulators (AVR).