Across two studies, we directly test the widely held tenet in the scholarship of organizational citizenship behavior (OCB) that individuals choose to engage in OCB as a result of felt obligations to reciprocate. We further examine how obligations to reciprocate operate against a backdrop of relevant contextual factors (accountability) and individual differences (proactive personality and interpersonal skill). Using an experimental method, we find evidence supporting the proposition that reciprocity obligations increase OCB engagement and that these effects are amplified by contexts high in accountability and when individuals possess high levels of proactive personality. In a subsequent field study, we find further corroborating evidence for the effects of reciprocity obligations on OCB and reaffirm the moderating influences of proactive personality and accountability. Overall, the convergent evidence supports the causal relationship between reciprocity obligations and OCB, as well as explicates the conditions under which this foundational effect operates across individuals and varying contexts.