What is considered to be fair depends on context-dependent expectations. Using a modified version of the Ultimatum Game, we demonstrate that both fair behavior and perceptions of fairness depend upon beliefs about what one ought to do in a situation—that is, upon normative expectations. We manipulate such expectations by creating informational asymmetries about the offer choices available to the Proposer, and find that behavior varies accordingly. Proposers and Responders show a remarkable degree of agreement in their beliefs about which choices are considered fair. We discuss how these results fit into a theory of social norms.