Even if its constituent members still define particular positions and pursue at times somewhat independent policies, the EU acts increasingly in important areas as the unified federal state many have long wanted it to be. It may have come into being in response to practical problems, and pragmatic considerations are likely to ensure its continued consolidation, but its most committed champions have also presented it as the realization of an idea, as a longstanding project finally fulfilled. What is the idea that a federal European state can claim to embody or represent or be animated by? How well do the various versions of the idea that have been articulated so far fit the current and emerging reality of the EU? Attention in the article focuses especially on the pan-European movement that emerged after the unprecedented destruction of World War I.