The proliferation of power electronics-based devices and equipment has significantly affected the power quality of the grid, which changes its sinusoidal nature through adding harmonic distortion. Power electronics applications have penetrated several venues in our life which increase the share of non-linear loads compared with linear loads, and hence degrades the power quality of the grid. Simultaneously, power electronics-based loads are sensitive to harmonic distortion. In order to cancel out or mitigate harmonics and their effects, active power filters, which will be discussed in this chapter, can be employed. Wiley Online library