The second edition provides thorough, up-to-date coverage of the analytical foundations of various aspects of nonlinear systems. This includes details on existence and uniqueness of solutions and approximate analysis methods. Reflecting the increasing importance of digital computers, the author has included a discussion of discrete-time systems in the chapters dealing with Lyapunov stability and input-output stability. Several applications of nonlinear system theory are included throughout the book, including stability and convergence of adaptive identifiers, stability of a class of electro-mechanical systems, a separation theorem for deterministic nonlinear systems, and more.