The purpose of this book is to illustrate to students both the techniques used in advanced analysis of physical systems and the reasons why these techniques work. Topics include infinite series and product expansions, asymptotic expansions, complex analysis, data fitting and physical models, integral transforms and their use in the solution of differential equations, statistical mechanics, finite and infinidimensional linear algebra, and the solution of the wave equation in one and two dimensions. This revised and updated edition contains all of the material from the first edition (corrected and expanded, especially in the chapter on orbits) as well as two new chapters, on complex variables and integral transformations. There are problems after each section, and answers to selected problems appear at the end. Chapter summaries have also been added at the end of each chapter.