This book presents the basis for designing a control strategy for Shunt Active Power Filters used for the compensation of harmonic currents consumed by nonlinear loads. The design of the controller is carried out using the interconnection and damping assignment technique. The control objective is to inject the adequate compensation current into the power system, so that the grid current is sinusoidal and balanced, regardless of whether the grid voltage is distorted or unbalanced. This application uses a design methodology based on interconnection and damping assignment that allows trajectory tracking control because the references of the compensating currents are variable, and they depend on the performance of the load and the grid. References of the compensation currents are calculated by using Instantaneous Active-Reactive Power Theory.