This book presents theoretical and application topics in power quality in distribution systems.With this book we wished to create a resource that is relevant to the needs of the working Power System engineers by helping bridge the theory and simulation work. A Power quality problem is an occurrence manifested as a nonstandard voltage, current or frequency that results in a failure or a mal-operation of end use equipments. Utility distribution networks, sensitive industrial loads and critical commercial operations suffer from various types of outages and service interruptions which can cost significant financial 1oss. With the restructuring of Power Systems and with shifting trend towards distributed and dispersed generation, the issue of Power Quality is going to take newer dimensions. In developing countries like India, where the variation of power frequency and many such other determinants of power quality are themselves a serious question, it is very vital to take positive steps in this direction. The present work is to identify the prominent concerns in this area and hence the measures that can enhance the quality of the power are recommended.