Forthcoming in the Max Planck Yearbook of United Nations Law (27) THE INTERNATIONAL LAW COMMISSION AND THE DEVELOPMENT OF INTERNATIONAL MIGRATION LAW BY Rodolfo Ribeiro C. Marques 1 Abstract: The International Law Commission (ILC) is often praised for successfully codifying key areas of international law, such as the law of treaties, the law of diplomatic and consular relations, and the law of responsibility. However, its contribution to the development of the law on areas that were not directly within its purview is frequently overlooked. International migration law seems to be a case in point. This article assesses the engagements of the ILC with international migration law in three main areas. It starts by discussing the early efforts of the Commission to codify the law of asylum, placing especial emphasis on the reasons behind, and the lessons one may learn from its failure to do so. The article then examines the work of the ILC on the law of nationality, including on the elimination and reduction of statelessness, state succession, and finally diplomatic protection. Lastly, it analyses the Commission’s attempts to systematize the law of admission and sojourn of non-nationals in its 2014 Draft Articles on Expulsion of Aliens. While the ILC has been helping to consolidate and clarify the position of international law on migration, its engagements with the field have laid bare the many political sensitivities evoked by any attempts to curb states’ discretion in this domain. The article thus paints a more complicated picture about the tensions between codification and progressive development in such a contested area of the law. Keywords: International Law Commission – customary international law – codification and progressive development – international migration law 1 PhD Researcher in International Law at the Geneva Graduate Institute. E: rodolfo.ribeiro@graduateinstitute.ch. 1 Electronic copy available at: https://ssrn.com/abstract=4816199