State courts have a responsibility to consider international human rights norms and other transnational law in rendering state constitutional decisions. This responsibility is drawn from several sources: the nature of federalism, the nature of the international system, and individual states’ laws and legal history. Where the United States has a formal obligation to comply with international law, the United States Constitution’s Supremacy Clause requires state courts to consider transnational authority. Indeed, without subnational attention to human rights norms, the international legal system fails under the weight of the “implementation gap” between national obligations and their implementation on the state level. Even absent a formal mandate, however, state courts should consider transnational sources when interpreting their constitutions. State court judges may find direct support for considering transnational sources in the constitutional and social history of the provisions being construed, bringing this approach inside the fold of traditional methodologies of constitutional interpretation. Furthermore, transnational law can inform the meaning of state constitutional grants that have no federal analogues but that are similar to international human rights law and to provisions of modem constitutions around the world. The United States Constitution, which textually focuses on limiting government action, may yield no guidance to state courts asked to interpret, for example, the substantive meaning of positive rights to “health,” “education,” or “welfare.” In such an instance, international norms articulated in transnational law may be a singularly important guide to the substantive content of the provisions. Though courts and scholars have paid significant attention to state constitutional provisions that have no obvious federal analogues in their efforts to establish the outlines of an independent state jurisprudence, they have seldom considered the role that transnational law might play in judicial review of these provisions. While federal judicial citation of transnational authority has sparked considerable debate in recent years, state court consideration of transnational sources should be much less controversial. First, the relatively populist structure of state governmental institutions, including state courts, undermines concerns that one branch might foist improper “foreign” views on the others unchecked. Second, institutional infighting between the federal branches-for example, over what constitutes an exercise of the foreign affairs power-has no parallel at the state level.