The Oxford Handbook of Prosocial Behavior provides a comprehensive review of the current literature on when and why people act to benefit others. It provides a comprehensive overview of the field to give both the casual reader and the neophyte to the field some perspective about fundamental questions (what, why, when, and who) relative to prosocial behavior. Taking a multi-level approach, the chapters represent the broad spectrum of this multi-faceted domain. Topics range from micro-level analyses involving evolutionary and comparative psychological factors to macro-level applications, such as reducing intergroup conflicts and ethnic genocide. Between these extremes, the contributors—all internationally recognized in their field—offer their perspectives on developmental processes that may predispose individuals to empathize with and respond to the needs of others, individual differences that seem to interact with situational demands to promote helping, and the underlying motivations of those helping others. They explain volunteerism, intragroup cooperation, and intergroup cooperation to move the analysis from the individual to group-level phenomena. They extend the consideration of this topic to include support of pro-environmental actions, means to encourage participation in medical clinical trials, and the promotion of world peace. The ways that gender, interpersonal relationships, race, and religion might affect decisions to give aid and support to others are also addressed. The final chapter offers a unique view of prosocial behavior that encourages researchers and readers to take an even broader consideration of the field to search for a prosocial consilience.