Abstract The European Court of Justice (ECJ) serves, among other things, as a constitutional court for the EU. This means that it possesses the legal right to strike down both EU and national laws it deems irreconcilable with treaty provisions. In the present article, we shall draw on Hans Kelsen's theory of democracy to argue that the ECJ's competence to review and invalidate legislation is, in fact, indispensable for the democratic legitimacy of the EU's legal system as a whole.