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 andor first year graduate students, the book also serve as a reference for researchers and practicing engineers in industry.