What role did the Roman legal concept of res nullius (things without owners), or the related concept of terra nullius (land without owners), play in the context of early modern European expansion? Scholars have provided widely different answers to this question. Some historians have argued that European claims based on terra nullius became a routine part of early modern interimperial politics, particularly as a response by the English and French crowns to expansive Iberian claims supported by papal donations. Others have countered that allusions to terra nullius marked a temporary phase of imperial discourse and that claimants relied more often on other rationales for empire, rarely mentioning res nullius or terra nullius and often explicitly recognizing the ownership rights, and even the sovereignty, of local polities and indigenous peoples.In sorting out these arguments and counterarguments about res nullius and terra nullius, we find that scholars on both sides of the debate have relied on relatively unexamined assertions about the Roman legal concepts and the way they were being used in and outside early modern Europe. A common error is to conflate the idea that Europeans were deeply influenced by Roman law with the assumption that they were very familiar with Roman law concepts. Scholars' assessments of terra nullius tend also to collapse multifaceted arguments and actions taking place at many levels of imperial activity, assuming, for example, the existence of direct and clear connections between the writings of jurists and