In this work, Nobel Laureate Steven Weinberg combines his physical insight with exposition to provide an introduction to quantum field theory. Volume 2 offers an account of the methods of quantum field theory, and how they have led to an understanding of the weak, strong and electromagnetic interactions of the elementary particles. The presentation of modern mathematical methods is interwoven with accounts of the problems of elementary particle physics and condensed matter physics to which they have been applied. Topics include the Batalin-Vilkovisky formalism and its application to renormalization and anomalies in gauge theories; the background field method; the effective field theory approach to symmetry breaking; critical phenomena; and superconductivity. The book also contains examples and insights from the author's experience as a leader of elementary particle physics.