The true designer of the High Authority of the European Coal and Steel Community (ECSC) might have been a French professor of international law, Paul Reuter (1911–1990). Then working in the shadow of Jean Monnet, he became one of the leading experts in public international law in France from the late 1950s on and also served on the International Law Commission. It was not his style to develop a fully-fledged theory of functionalism, but he paid the utmost attention to the ‘functions’ of international organizations. While demonstrating a certain reluctance towards some consequences associated with functionalism, he expressed no disdain for a lite version of ‘constitutionalism’. Discretely, Reuter outlined a balancing between ‘functionalism’ and ‘constitutionalism’. He more insistently elaborated on the respective role of experts and policy-makers.