The United Nations International Law Commission occasionally deals with the law relating to international organizations. A well-known example is its work in preparation of the Vienna Convention on the Law of Treaties between States and International Organizations or between International Organizations of 1986. It is less well-known, but perhaps more important for the practice of international organizations, that the Commission has in recent years also addressed other relevant issues in this field. Those include the responsibility of international organizations (2011), the role which the practice of international organizations may play in the interpretation of their constituent instruments (2018) and in the formation of customary international law (2018), as well as considerations on whether the topic ‘Settlement of disputes to which international organizations are parties’ (2016) should be put on its agenda. This chapter reflects the 2018 aiib Law Lecture, summarizing the work of the Commission on these aspects of the law of international organizations and engages in some general reflections.