On 30 October 2024, our Scientific Director and Professor of Fundamental and Human Rights at the University of Vienna, Michael Lysander Fremuth, gave a lecture on the international law issues of a war of aggression. The lecture was part of the event ‘Ukraine in the Russian War of Aggression’ organised by Wolfgang Mueller, Deputy Director of the Institute, and Ihor Zhaloba at the Institute of Eastern European History at the University of Vienna. Fremuth explained, why conducting a war of aggression constitutes a particularly serious violation of international law and disregards the central idea of the peace order that was intended to be created in 1945 with the founding of the United Nations. He also pointed out various violations of human rights and international humanitarian law and discussed the legal aspects of the reactions. The lecture was followed by an intensive discussion, which was characterised by great interest from the audience.