Abstract: Modern advocates of corporate self-regulation have drawn unlikely inspiration from the Middle Ages. On the traditional view of history, medieval merchants who wandered from fair to fair were not governed by domestic laws, but by their own lex mercatoria, or "law merchant." This law, which uniformly regulated commerce across Europe, was supposedly produced by an autonomous merchant class, interpreted in private courts, and enforced through private sanctions rather than state coercion. Contemporary writers have treated global corporations as descendants of these itinerant traders, urging them to replace conflicting national laws with a transnational law of their own creation. The standard history has been accepted by legal scholars across the ideological spectrum, by economists and political scientists, and by those drafting new regimes to govern Internet commerce. This Article argues that the traditional view is deeply flawed. Returning to the original sources - especially the court rolls of the fair of St. Ives, the most extensive surviving records of the period - it demonstrates that merchants in medieval England were substantially subject to local control. Commercial customs and substantive laws varied significantly across towns and fairs, and did not constitute a coherent legal order. The traditional interpretation has been retained, not for its accuracy, but for ideological reasons and for its long and self-reinforcing pedigree. This Article takes no position on the merits of shielding multinational actors from domestic law; it merely denies that the Middle Ages provide a model for such policies.