This book integrates several streams of nonlinear control theory to address the feedback stabilization problem constructively. It combines analytic, geometric, and asymptotic concepts to design solutions for a wide range of nonlinear phenomena and structures. The main tool is passivity, which connects all chapters as a common thread. Passivity properties are induced by feedback passivation designs, which were previously restricted to weakly minimum phase systems with relative degree one. The authors have developed recursive designs that overcome these restrictions, making the approach applicable to a broader class of nonlinear systems characterized by feedback, feedforward, and interlaced structures. The book is divided into two major parts. The first part covers the basic nonlinear system concepts—passivity, optimality, and stability margins—in Chapters 2 and 3, presenting them in a novel way as design tools. The second part, consisting of Chapters 4, 5, and 6, constructs design procedures for cascade systems and then extends these to larger classes of nonlinear systems. These procedures result in feedback systems with optimality properties and stability margins. The book differs from other nonlinear control texts by being more design-oriented and broadening the class of systems and design tools. It is suitable for graduate students, control engineers, and applied mathematicians interested in control theory. The book is self-contained and accessible with a basic knowledge of control theory and nonlinear systems. The authors introduce most concepts through examples and illustrate design applications on several practical physical models. The book can be used as a first-level graduate course on nonlinear control or as collateral reading for a broader control theory course. The main recursive procedures—backstepping and forwarding—are introduced in Chapter 6, with backstepping being known from previous works and forwarding being a new procedure developed by the authors. The book is a result of postdoctoral research by the first two authors at the Center for Control Engineering and Computation, University of California, Santa Barbara. It benefited from the support of various institutions and individuals, including Ford Motor Company, BAEF, FNRS, Belgium, and NSF, AFOSR, and the authors' families.This book integrates several streams of nonlinear control theory to address the feedback stabilization problem constructively. It combines analytic, geometric, and asymptotic concepts to design solutions for a wide range of nonlinear phenomena and structures. The main tool is passivity, which connects all chapters as a common thread. Passivity properties are induced by feedback passivation designs, which were previously restricted to weakly minimum phase systems with relative degree one. The authors have developed recursive designs that overcome these restrictions, making the approach applicable to a broader class of nonlinear systems characterized by feedback, feedforward, and interlaced structures. The book is divided into two major parts. The first part covers the basic nonlinear system concepts—passivity, optimality, and stability margins—in Chapters 2 and 3, presenting them in a novel way as design tools. The second part, consisting of Chapters 4, 5, and 6, constructs design procedures for cascade systems and then extends these to larger classes of nonlinear systems. These procedures result in feedback systems with optimality properties and stability margins. The book differs from other nonlinear control texts by being more design-oriented and broadening the class of systems and design tools. It is suitable for graduate students, control engineers, and applied mathematicians interested in control theory. The book is self-contained and accessible with a basic knowledge of control theory and nonlinear systems. The authors introduce most concepts through examples and illustrate design applications on several practical physical models. The book can be used as a first-level graduate course on nonlinear control or as collateral reading for a broader control theory course. The main recursive procedures—backstepping and forwarding—are introduced in Chapter 6, with backstepping being known from previous works and forwarding being a new procedure developed by the authors. The book is a result of postdoctoral research by the first two authors at the Center for Control Engineering and Computation, University of California, Santa Barbara. It benefited from the support of various institutions and individuals, including Ford Motor Company, BAEF, FNRS, Belgium, and NSF, AFOSR, and the authors' families.