The creation of Economic and Monetary Union (EMU) in Europe challenges much of what we have come to take for granted about states and the components of sovereignty. What does the willingness of twelve European Union (EU) members to abandon their own currencies mean for the nation-states of Europe? Does the Euro automatically imply further political development at the EU level? To address these questions, this paper parses out the role that national currencies play in statebuilding with reference to the nineteenth century American experience. Just as US federal authorities engaged in a political project to wrest control over money from subnational authorities to the center and unify the currency, so have the dynamics of currency unification in the EU involved important conflicts over the location of the legitimate exercise of control and rule. In particular, I highlight the role of war and market integration in prompting currency consolidation, and the importance of linkages between money and fiscal capacity for statebuilding, and apply the analytical lessons learned from the US experience to the case of the Euro.