behavior in terms of increasing group well-being. We report a decision and game theoretical analysis of efficacy in step-level public goods (SPGs). Previous research shows a positive relation between efficacy and contributions to SPGs and explains this relation by a purely motivational account. We show, however, that from a decision and game theory perspective an increasing relationship is not general, but only follows from very specific assumptions about players’ information and beliefs. We offer 3 examples of how the predicted efficacy–contribution relation depends on players’ information and beliefs. We discuss the implications of our results for the social psychology of efficacy in social dilemmas.