Three terms are commonly used in the broad research area that investigates positive interpersonal action: prosocial behavior, helping behavior, and altruism. "Prosocial behavior" is the broadest of the three; it refers to any behavior that can be construed as consistent with the norms of a given society. Thus, murder, when enacted on behalf of one's country on a battlefield, is as prosocial a behavior as intervening to prevent a crime. "Helping behavior" refers simply to any behavior that provides some benefit to its recipient. "Altruism" is the narrowest of the three concepts. Altruism is behavior that not only provides benefits to its recipient but also provides no benefits to the actor and even incurs some costs. If one conceives of psychological rewards as benefits to the actor, this definition of altruism is so narrow that it excludes virtually all human behavior. Hence, many social psychologists maintain simply that...