Pulse width modulation is a form of pulse coding where the modulated signal contains a chosen frequency or band of frequencies as the main components plus harmonics of very high order that can be easily filtered. Even though PWM originated in telecommunication systems, it is now very common in power electronic circuits: dc to dc converters, dc to ac and wave-shaping circuits. In its simplest form we have a single frequency coded on the PWM signal known as sinusoidal Pulse Width Modulation. In this chapter a number of signals are pulse width modulated: a unipolar signal for a sine wave a unipolar signal for a rectified sine wave, a composite signal consisting of a rectified sine wave and its derivative, and a bipolar signal for a sine wave. For each signal a 'component switching function' is derived which gives a single pulse; the width of the pulse is set according to its position. The PWM signal is the sum of m such component switching functions.