Sixteen months after rejecting the EU’s Lisbon Treaty, Ireland has held a referendum with a vast majority approving it. This is big news because only Poland and the Czech Republic are left to ratify the document, which both of their parliaments have already approved. The idea of a European federation grows ever closer to reality. Opponents of the treaty worry that this would undermine national sovereignty. Yet I think it is time that we start moving away from the premise that national sovereignty is an irreducible component of international politics. Even though nation states are the main actors in the international system that exists today, it will be interesting to see whether this begins to change once more of them become bound in such unions and federations.