This paper presents a theory of norm enforcement. Dominant accounts explain norms by referring to their consequences. On this view, norms are enforced when they increase the welfare of group members. While useful, such approaches do not explain much of what we observe. The theory developed here argues that while sanctioning consequences are part of the explanation, characteristics of social relations – in particular, interdependence – have significant effects. The results show that the effects of sanctioning benefits and costs vary depending on the level of interdependence between group members. Further, interdependence itself has direct effects on both metanorms and norms. These results reveal that variation in interdependence may lead to under-enforcement of norms that contribute to group welfare, or over-enforcement of norms that are harmful. The research therefore suggests that explanations that focus on the direct consequences of enforcement, and that fail to incorporate characteristics of social relations, may produce inaccurate predictions. Accordingly, understanding the role of social relations is essential for explaining norms.