This chapter reviews the main classes of circuits and devices that are currently used, emphasizing the basic operating principles and characteristics. The three-pulse rectifier supplies a resistive load in series with a filter inductor, the inductor being large enough to ensure that the load current is continuous and ripple-free. The circuit is a half-wave rectifier, with each supply line being connected through a single diode to the top of the load, the neutral wire forming the return path. To enhance the characteristics of the six-pulse rectifier, reducing the input current harmonics and the output voltage ripple, multiple rectifiers may be combined with a phase-shifting device, a transformer or an autotransformer. Three inverter legs are connected together to synthesize a set of three-phase voltages from a dc source. The circuit has two operating modes, either the transistors operate at the same frequency as the ac output waveforms, known as quasi-squarewave or six-step operation, or alternatively the devices operate at a much higher frequency than the ac output using a form of sinusoidal pulse width modulation. © 2005 Elsevier Ltd All rights reserved.