When the first edition of this book was published, most control theorists considered the subject of nonlinear systems a mystery. Since then, advances in the application of differential geometric methods to nonlinear analysis have matured to a stage where every control theorist needs to possess knowledge of the basic techniques. The second edition provides a rigorous mathematical analysis of the behavior of nonlinear control systems under a variety of situations. It develops nonlinear generalizations of a large number of techniques and methods widely used in linear control theory. It contains three extensive chapters devoted to the key topics of Lyapunov stability, input-output stability, and the treatment of differential geometric control theory. Moreover, valuable reference material included in these chapters is unavailable elsewhere. The text also features a large number of problems that allow readers to test their understanding, and self-contained sections and chapters that make particular topics more accessible.