In this article, the authors develop the self-concern and other-orientation as moderators hypothesis. The authors argue that many theories on work behavior assume humans to be either self-interested or to be social in nature with strong other-orientation but that this assumption is empirically invalid and may lead to overly narrow models of work behavior. The authors instead propose that self-concern and other-orientation are independent. The authors also propose that job performance, prosocial behavior, and personal initiative are a function of (a) individual-level attributes, such as job characteristics when employees are high in self-concern, and (b) group-level attributes, such as justice climate when employees are high in other-orientation. Three studies involving 4 samples of employees from a variety of organizations support these propositions. Implications are discussed for theory on work behavior and interventions geared toward job enrichment and team-based working.