Lecture summary: An analogy between States and international organizations has characterised the development of the law that applies to intergovernmental institutions on the international plane. That is best illustrated by the work of the International Law Commission on the treaties and responsibility of international organizations, where the Commission for the most part extended to organizations rules that had been originally devised for States in the 1969 Vienna Convention on the Law of Treaties and 2001 Articles on the Responsibility of States for Internationally Wrongful Acts. The talk, based on a recently published research monograph, will reflect on the foundations of the assumption that the two main categories of international legal subjects are analogous for certain purposes, and discuss the elusive position that international organizations occupy in the international legal system. Dr Fernando Lusa Bordin is a University Lecturer in International Law at the University of Cambridge and is a Fellow of the Lauterpacht Centre.