The essay concerns the reservations attached to the declarations accepting the compulsory jurisdiction of the two International Courts. As early as during the 1920s when States consented to the compulsory jurisdicition of the first World Court they attached limitations on, conditions or reservations to their declarations of acceptance. For these declarations, there were no rules whatever prescribing any sort of uniformity or similarity of content in any aspects, and States formulated more and more complicated restrictions to their declarations of acceptance. After the International Court of Justice had been established, States continued the practice of attaching reservations to declarations of acceptance and, moreover, increased the number thereof, “inventing” more and more complicated reservations. Quite a few of such reservations placed much more limitations on the Court's compulsory jurisdiction than the interwar declarations of acceptance had done and a no small part of them left loopholes of escape from the jurisdiction recognized. In analysing the problems of permissible reservations, the author refers to the rules and criterias developed in international treaty law on the reservations to multilateral treaties and to the jurisprudence of the two Word Courts. She concludes that the declarations of acceptance are unilateral acts and the States are free to attach any reservation to their declarations of acceptance.