Rights interpretation is intimately bound up with questions about the basis of rights. Within the context of American constitutionalism, questions about the universality of rights are especially pressing. Does constitutional interpretation properly involve reasoning from universalistic principles, or should it be limited to particularly American preferences, traditions, texts, and practices? This study examines how the Supreme Court justices have approached this question. To the extent that public law studies consider the Court's use of universalistic reasoning, they typically fall under the rubric of "natural law" jurisprudence in a discrete issue area or time period. "Natural law" often carries associations, such as an emphasis on property rights, that may unnecessarily constrict the field of investigation. This dissertation is not aimed at a pre-determined version of universalistic jurisprudence, or at a single time period or issue area. Rather, it shows that universalistic reasoning has played an important role in the Court's rights jurisprudence across a wide range of issue areas from the Court's earliest rights decisions to the present day. With an expanded focus, this study demonstrates patterns and shifts in the use of universalistic reasoning, and axes of disagreement between the justices, that transcend boundaries between issue areas. By exploring the Court's jurisprudence through the prism of questions about the grounding of rights, this dissertation sheds light both on constitutional law and on fundamental tensions between universalistic and particularistic bases of rights.