Lecture summary: A question that is often under-theorised, or perhaps more accurately, is taken for granted, is the systematicity of international law. The systemic nature of international law too often is simply presumed, and rests on a vision of international law as merely a body of rules. In this lecture, an alternative account of international law's systematicity will be advanced, one which encompasses not only the systemic character of international legal rules, but instead portrays international law as a socially-constructed system, in which certain key actors play a particularly influential role.