On 5 May 2020, the German Constitutional Court declared that the bond-buying programme of the European Central Bank was ultra vires (exceeding its competences) and therefore, explicitly challenged the authority of the European Court of Justice. Joseph Weiler, University Professor at NYU School of Law and Director of the Jean Monnet Center for International and Regional Economic Law and Justice, and Beatrice Weder di Mauro, Professor of International Economics at the Graduate Institute, discuss how this German court ruling affects not only the monetary policy in the eurozone but also the future of the rule of law in Europe.