Legal personality is generally understood as the capability to be – in traditional anthropomorphic terms – ‘the bearer of legal rights and obligations’. Legal personality is a structuring tool in legal systems, not least that of international law, as it indicates who are the participants. This chapter considers the concept of ‘legal personality’ in two different roles, which are mutually constitutive. The concept works as an epistemic tool in theoretical reflections on the workings of international law, while at the same time it denotes a doctrinal category within the system of international law. The chapter takes both functions into account, with a concomitant shifting between levels of analysis, and a look also at the actual candidates for international legal personality which over time have emerged in different political contexts. The chapter discusses a sequence of moments in the development of the form and use of the concept that seem especially significant. While the chapter thus gives a diachronical account of the concept, the identified moments in its development are also continuing and coexisting aspects. For example, while it is true that an intense concern for the state as the sole legal person in international law came to the fore in the second half of the nineteenth century, the central position of the state is also an important element in today’s discourse on international legal personality.