Book excerpt: The Power of Nonviolence, written by Richard Bartlett Gregg in 1934 and revised in 1944 and 1959, is the most important and influential theory of principled or integral nonviolence published in the twentieth century. Drawing on Gandhi's ideas and practice, Gregg explains in detail how the organized power of nonviolence (power-with) exercised against violent opponents can bring about small and large transformative social change and provide an effective substitute for war. This edition includes a major introduction by political theorist, James Tully, situating the text in its contexts from 1934 to 1959, and showing its great relevance today. The text is the definitive 1959 edition with a foreword by Martin Luther King, Jr. It includes forewords from earlier editions, the chapter on class struggle and nonviolent resistance from 1934, a crucial excerpt from a 1929 preliminary study, a biography and bibliography of Gregg, and a bibliography of recent work on nonviolence.