PWM inverters are widely used in industrial, commercial and residential application such as motor drives. In three-leg inverters for three-phase applications the occurrence of common mode voltage is inherent due to asymmetrical output pulses. It has been found that the high dv/dt and high switching frequency together with the common mode voltages generated by PWM inverters have caused many adverse effects such as shaft voltage, bearing current, leakage current, motor terminal over voltage and electromagnetic interference (EMI). The EMI generated by such systems is increasingly causing concerns, as the electromagnetic compatibility (EMC) regulations become more stringent. In order to comply with these international EMC regulations, an EMI filter is often necessary. The major objective of this book is to investigate and suppress of the adverse effects of PWM inverters. Theoretical analysis of all the adverse effects is presented in this book. Several passive and active EMI filters and their design procedures are proposed and performed. The experimental results of applying these novel filters are presented.