The field of prosociality is flourishing, yet researchers disagree about how to define prosocial behavior and often neglect defining it altogether. In this review, we provide an overview about the breadth of definitions of prosocial behavior and the related concept of altruism. Common to almost all definitions is an emphasis on the promotion of welfare in agents other than the actor. However, definitions of the two concepts differ in terms of whether they emphasize intentions and motives, costs and benefits, and the societal context. In order to improve on the conceptual ambiguity surrounding the study of prosociality, we urge researchers to provide definitions, to use operationalizations that match their definitions, and to acknowledge the diversity of prosocial behavior.
