This book is the first systematic examination of the impact of reconciliation on restoring and maintaining peace following civil and international conflicts. Through eleven comparative case studies of civil war and more than 20 of international conflict, it constructs a surprising explanation for why and when reconciliation restores social order. The civil war cases reveal that successful reconciliation is associated with a process of national forgiveness, not merely negotiated settlement. All successful cases followed a four-step pattern of public truth telling, justice short of revenge, redefinition of the identities of former belligerents, and the call for a new relationship. The book argues that success is not solely the result of rational choice. It proposes a hypothesis, grounded in evolutionary psychology, that to restore social order we use emotional cognitive techniques that have evolved to ensure human survival. On the international level, reconciliation was unsuccessful when part of a forgiveness process, a result consistent with realist notions of the limits of international society and the power of national identities. Reconciliation was, however, successful in bringing about peace when part of a "signalling" model - a costly, novel, voluntary, and irreconcilable concession in a negotiated bargain. The book's approach, integrating emotion with reasoning and linking political science to scientific research in other disciplines, particularly biology and neuroscience, has broad implications for social science theory.