Cities are increasingly recognized as actors that participate in the implementation and even in the creation of international law. On the occasion of the publication of the Research Handbook on International Law and Cities, Moritz Baumgärtel speaks to the volume’s lead editors and pioneering scholars in the field: Janne Nijman, Professor of History and Theory of International Law at the University of Amsterdam, and Helmut Aust, Professor of Law at the Freie Universität in Berlin. In their conversation, they talk about how cities’ actions became a topic first in their own research, and then in international law more generally—and why people from outside the discipline should care about this development in international law. They also go through some of the examples where cities’ influence has been particularly pronounced, as well as the response of states to cities challenging (or at least negotiating) their sovereignty.The Research Handbook on International Law and Cities was published by Edward Elgar in autumn 2021; the introductory chapter by Janne Nijman and Helmut Aust can be accessed freely (https://www.elgaronline.com/view/edcoll/9781788973274/9781788973274.00006.xml). The ILA City Reports are available on the website of the T.M.C. Asser Institute (https://www.asser.nl/global-city/ila-city-reports/). This episode has been produced with the assistance of Sithis Yim Samnang.