This dissertation draws interdisciplinary insights from philosophical discourse on collective entities in order to advance a refined conception of international organizations in public international law. It suggests that current efforts to theorize international organizations face severe limitations in formulating a convincing legal theory of these institutions and their legal personality. As a result, ambiguity lingers on a number of important legal issues, such as the extent to which international organizations are bound by the same rules of customary international law as states, and their capacity to contribute directly to custom’s formation. After exposing the limits of current scholarship, this dissertation moves on to explore its core philosophical assumptions. It suggests that the prevailing approach operates on the basis of troublesome assumptions which substantially curtail scholars’ ability to fully conceptualize the nature of international organizations. These assumptions pertain to the legal personality of the state itself—the entity that is supposed to form the building block of international organizations. Despite the emergence of newer theoretical approaches over the years, scholars continue to operate on a rough premise of state anthropomorphism. According to this popular, though dated notion, the state can be analogized to the individual human being. Modelling the state as a soulful or organic entity distorts the theorizing effort regarding international organizations. Anthropomorphic interpretations of the state’s legal personality suggest that international organizations are either artificial, and thus somehow less real entities than states, or that they too should be theorized as soulful or organic entities on par with states. Trapped between the opposite ends of this crude binary, the discipline is left with unappealing, and ultimately problematic, avenues for theorizing international organizations. This dissertation delves into the philosophical debates surrounding the notion of collective entities in order to overcome this binary. On this basis, it proposes a more nuanced conceptualization of international organizations. Rather than trying to compare and contrast states and international organizations for all intents and purposes, scholars should instead think of both entities as manifestations of public authority. This revised theoretical framework can then lay the groundwork for addressing key analytical problems in public international law regarding these institutions.