This chapter is about law-making by international organizations (IOs), or what I call “delegated law-making” for short. It is a complex phenomenon, not least because the scope of matters covered by both “law-making” and “delegation” is contested. Although some intergovernmental organizations have been empowered to make law explicitly, the relationship between states and the organizations they create is often more complicated than the term delegation connotes. Various strands of international law (IL) and international relations (IR) theory shed light on this relationship, and, as such, delegated law-making is a good laboratory for exploring thevalue of cross-disciplinary theorizing. The chapter begins with the concept of delegation, arguing that it comes in three forms when applied to IOs: explicit, implied, and attenuated. The second section, “Law in Its Infinite Variety” is devoted to law-making. I present a pluralistic conception of law that includes five distinct types of IO acts or instruments: treaty law, legislation and regulation, executive decisions, soft law, and judge-made law. I provide examples to illustrate the extentto which delegation tends to be implied and attenuated, as well as explicit.