The prevailing justification for trademark law depends on economic arguments that cannot account for much of the law's recent development, nor for mounting empirical evidence that consumer decisionmaking is inconsistent with assumptions of rational choice. But the only extant theoretical alternative to economic analysis is a Lockean "natural rights" theory that scholars have found even more unsatisfying. This Article proposes a third option. I analyze the law of trademarks and unfair competition as a system of moral obligations between producers and consumers. Drawing on the contractualist tradition in moral philosophy, I develop and apply a new theoretical framework to evaluate trademark doctrine. I argue that this contractualist theory holds great promise not only as a descriptive and prescriptive theory of trademark law, but as a framework for normative analysis in consumer protection law generally.