"Dressing the Law" explores the relationships between appearance, identity, and status across the Spanish Empire. My dissertation charts the development of socio-racial sumptuary legislation – statutes that barred select groups from wearing certain dress or using particular items – from 1600 to 1700 in Seville, Mexico City, and Lima. As three of the empire's most important trade centers, each city experienced unprecedented levels of interracial mingling by the start of the seventeenth century. In order to evaluate such legislation holistically, I incorporate laws that targeted groups traditionally kept apart in historiography. This includes religious converts, pardos and mulatos (castas), and natives. My investigation thus asks two central questions. How did regional communities regulate dress to restrict the assimilation of different ethnic populations? How did such local actions influence the production of new imperial edicts? As diversity proliferated in the Americas, I hypothesize that residents petitioned the Crown for aid in controlling dress in order to counteract increasingly blurred cultural distinctions. This analysis draws on administrative documents such as orders, complaints, and legal exemptions, royal decrees and petitions to the Crown, and Inquisition records. Utilizing a bottom-up perspective that emphasizes the active role of subjects in influencing legal production, I compare imperial and local sources to evaluate the dynamics that shaped such regulations throughout the empire. "Dressing the Law" thus dialogues with scholarship on both early modern identity formation and the socio-political organization of Spanish America. Ultimately, by analyzing the formative period of socio-racial sumptuary laws, this dissertation both clarifies how the trans-Atlantic legal network operated and reveals how the process of defining difference developed in the Spanish Empire.