Ever since the beginnings of mankind eons ago, the desire to control, regulate, and track even under persistent disturbances has been a dominating influence in the development of human civilization. It is so also in the development of Automatic Control Theory and its Applications. The subject of output regula­ tion occupies a central theme in all endeavors of theoreticians and practition­ ers alike. Yet there is no book or monograph that brings all essential modem developments on output regulation under a single cover. This book is intended to fill this void. Main topics that are brought together in this book include among oth­ ers, classical exact output regulation of linear systems along with its different facets of well-posedness, internal model principle, and structural stability; output regulation of linear systems with input amplitude and rate saturation constraints; output regulation with transient performance specifications; per­ formance issues (such as H2, H , L1 and others) with an output regulation oo constraint; generalized output regulation in which the set of tracking signals as well as the set of disturbances that act on the plant are broadened beyond those that are common in classical output regulation, and thus permitting us to deal with exact as well as almost output regulation under a variety of controllers, etc.