IEEE has defined Automatic Generation Control (AGC) as "the regulation of the power output of electrical generators within a prescribed area in response to change in system frequency, tie-line loading, or the relation of these to each other, so as to maintain the scheduled system frequency and/or the established interchange with other areas within predetermined limits." In this book, a comprehensive analysis of AGC of interconnected power systems has been carried out - both in traditional and deregulated environments. This book is intended as a reference for practising engineers and research students.