The members of a peaceful society rarely, if ever, engage in physical aggression, and correspondingly, they share a system of beliefs that eschews aggression and instead promotes harmonious, nonviolent interpersonal relations. This article provides a brief overview of peaceful societies and reviews the growing literature about them. It considers several theoretical issues. Viewing societies along a peacefulness-aggressiveness continuum is a useful way to visualize cross-cultural variability. Other topics considered include intracultural variation in peacefulness, within-group versus between-group peacefulness, changes in peacefulness of a society over time, and the multidimensional nature of aggression. It then focuses on the intriguing question of how peaceful societies manage to keep the peace. The discussion begins by highlighting how the presence of a belief system that promotes nonviolence is perhaps the single most critical feature that peaceful societies share with one another. Some of the ways that nonviolent belief systems contribute to peacefulness are examined, including child socialization practices that favor nonviolence over aggression, core values such as egalitarianism that are incompatible with the expression of violence, use of interpersonal avoidance, internalization of self-restraint against expressing anger and aggression, use of a variety of informal social controls, and third-party participation in conflict resolution. One important implication of research on peaceful societies is that humans are capable of creating and maintaining societies with very low levels of aggression. This statement is not utopian, because numerous peaceful societies actually exist. © 2008 Elsevier Inc. All rights reserved.