This 2nd edition provides an in-depth, up-to-date, unified, and comprehensive treatment of the fundamentals of the theory of active networks and its applications to feedback amplifier design. The main purpose is to discuss the topics that are of fundamental importance that transcends the advent of new devices and design tools. Intended primarily as a text in circuit theory in electrical engineering for senior and/or first year graduate students, the book also serve as a reference for researchers and practicing engineers in industry.A special feature of the book is that it bridges the gap between theory and practice, with abundant examples showing how theory solves problems. These examples are actual practical problems, not idealized illustrations of the theory. The topic on topological analysis of active networks is also expanded to benefit more discerning readers.