This article addresses the opportunities and challenges for researching the history of Indigenous custom during a period in which constitutional and legal reform have led to the recognition of customary law as an official framework for local governance and the administration of justice in Oaxaca, Mexico. The article begins by situating Oaxaca’s laws within the context of broader neoliberal reforms in Latin America characterized by the promulgation of multicultural constitutions recognizing the legal jurisdiction and cultural autonomy of Indigenous communities. Some Indigenous intellectuals, activists, and NGOs working in Oaxaca have declared this new administrative arrangement a victory for Indigenous rights to self-determination, arguing that customary law serves as a defensive wall against state and corporate incursions of many kinds. Other local Indigenous scholars have nuanced the custom-law and community-state oppositions, situating customary law—currently referred to as “Indigenous normative systems”—as historical and contested, and in dynamic interplay with relationships of power within and beyond the community. The article’s author considers these debates about custom’s ambiguous meanings and effects and reflects on how the recent context of legal reform nourishes the author’s own scholarship on the colonial period by providing a broad temporal, cultural, and political framework with which to understand its stakes. The author also explores how historians researching Oaxaca’s deep past can meet the interpretive demands of their discipline while being attentive to historical justice and engaging the communities whose ancestors occupy center stage in our histories.