This item starts with a general discussion on power quality, including definitions, terminology, and requirements. It further contains sections on the importance of power quality (which in the end all comes down to reducing the likelihood of interference, i.e., equipment not functioning as it should); some of the subjects that have been historically on the agenda within power quality (going back to harmonics and light flicker, which were on the agenda before the term power quality in its modern meaning was used, voltage dips, and several waves of interest for waveform distortion); the main aspects of power quality monitoring (different for variations and events); the most important power quality disturbances (voltage magnitude variations, fast voltage variations, voltage dips, voltage swells, interruptions, harmonics, interharmonics, supraharmonics, and transients) and an overview of power quality regulation (discussed around the regulatory dilemma).