Power quality is necessary for electrical systems to operate in their intended manner without any deterioration of performance. This book highlights the new emerging challenges of power quality due to the penetration of large-scale renewable energy generation technologies, the advances in nonlinear loads, the increased electricity demands in the deregulated market, and the recent requirements of smart grids that need better hierarchical design with enhanced quality, improved controllability, higher reliability, and security. Novel research that links the past, present and future of electrical power grids from a power quality perspective is also introduced. Topics include power quality definitions; frequency-domain power theory and metering of harmonic pollution responsibility; active and passive harmonic filters; shunt flexible AC transmission; power quality improvement using series FACTS; distributed generation systems; islanding scenario generation algorithm; decentralised voltage control in smart grids; techno-economic issues of power quality; economic robust programming for energy management systems; and future trends in power quality.