Over the past two decades, customary international law has become a hotly debated subject in the United States, giving rise to new theories on the relationship between international norms and the common law. However, simply because the applicability of customary international norms in U.S. courts has become foggy does not mean that the evolution of customary international norms has slowed, nor that parties in U.S. courts should be hesitant to argue new norms in U.S. state and federal jurisdictions. This Note argues that the right to an interpreter is a right recognized and protected by customary international law, and, as such, can be claimed by individuals in U.S. courts who have suffered a prejudicial violation. The right to an interpreter is generally viewed as a subsidiary right of the right to a fair trial; however, even as a subsidiary right, it is an important and necessary right that is well established by state practice and opinio juris. Moreover, the right is a more specified and definite norm of customary international law than the right to a fair trial and is thus more easily applicable in domestic jurisdictions, opening up the possibility for new customary international law claims to be made in U.S. courts. The recognition of the right to an interpreter as a norm of customary international law is important both in theory for the elucidation of international law and also in practice for individuals who have suffered a violation but lack an international forum in which they could vindicate their rights. The United States offers some of the strongest fair trial guarantees in the world, and, as a result, parties in U.S. courts can often look to the U.S. Constitution for protection of their due process and fair trial rights. However, in some circumstances, and as will be demonstrated with interpretation rights, international law may offer greater protection of specific fair trial rights, leaving individuals who are unable to argue these rights in U.S. courts vulnerable to a violation without an appropriate domestic remedy. Identifying the right to an interpreter as a right protected under customary international law consequently helps to provide greater protection of such rights for claimants in American courts, and may help to reignite the use of customary international norms in the U.S.This Note begins in Part II by arguing that the right to a fair trial is a general norm under customary international law established by state practice and opinio juris. However, the right to a fair trial is too vague and indefinite to be invoked successfully in national courts, and especially not U.S. courts which may apply a strict standard for customary international law norms after the Supreme Court’s decision in Sosa v. Alvarez-Machain. Part III finds that the right to an interpreter has sufficient state practice and opinio juris to be considered a right under customary international law independent of the general right to a fair trial, and is not as problematic as the right to a fair trial for application in U.S. courts. Finally, Part IV considers the potential of the customary international right to an interpreter for application in U.S. federal and state courts, arguing that the right to an interpreter likely provides an additional layer of protection for individuals who are insufficiently protected by interpretation standards in federal or state jurisdictions. Ultimately, this Note aims to cement the status of the right to an interpreter as a norm of customary international law, for potential application in both national and international tribunals by individuals who have suffered prejudicial violations of their rights.