In analogy to municipal law, the notion of personality is used in international law to distinguish between those social actors the international legal system takes account of and those being excluded from it. But owing to the peculiarities of the international legal system, there is no clearly established international law of persons. As a result, there are different positions on exactly which entities count as persons in international law, under what criteria personality is acquired and what specific consequences this status entails. This lack of clarity is disconcerting in itself. But it also influences the outcome in particular legal situations. In order to substantiate these claims, Part I of this book will first outline the presence and function of personality in international legal argument (1). It will then identify the different substantive positions on the concept and how one has to deal with them (2). Finally, the case will be made for the significance of the concept in legal practice even when personality is not directly addressed (3).