This collection of mostly original essays by scholars and Catholic Worker activists provides a systematic, analytical study of the emergence and nature of pacifism in the largest single denomination in the United States: Roman Catholicism. The collection underscores the pivotal role of Dorothy Day’s Catholic Worker movement in challenging the conventional understanding of just-war principles and the American Catholic Church’s identification with uncritical militarism. Also included are a study of Dorothy Day’s preconversion pacifism, previously unpublished letters from Dorothy Day to Thomas Merton, Eileen Egan’s account of the birth and early years of Pax, the Catholic Worker-inspired peace organization, and in-depth coverage of how the contemporary Plowshares movement emerged from the Catholic Worker movement.