The recent renaissance of work on conventions, informal institutions, and social norms has reminded us that between the state and individual choice is a network of informal social rules that are the foundation of our cooperative social life. However, even those who appreciate the importance of social norms are reluctant to say that they are about real morality. The first part of the essay examines why this is so. The problem, I suggest, is a widely-embraced view according to which moral judgment is an individual decision about a type of truth that is largely independent of social facts. I show that this popular conception undermines effective social norms and moral conventions. The second part of the essay analyzes the conditions under which effective conventions can be made consistent with diverse individual judgments as to what is morally acceptable–and so conventions can be understood to concern what is genuinely moral. The key, I argue, is the idea of a publicly justified morality as modeled by a hypothetical social contract.