This chapter deals with passive, active, and hybrid filters. Passive filters can be applied to the input and output of a power converter to reduce or eliminate unwanted current and voltage harmonic components. Active filters can be applied to a utility grid to reduce current and voltage harmonic components due to nonlinear loads. Hybrid filters are a combination of passive and active filter types. Each filter type is examined and solved problems and simulation results are presented to help the reader understand the theory presented in this chapter.