n this article, I seek a theoretically informed answer to the question of why in the period after 1993 the German government clamoured for a clarification of and a tightening of the rules governing the transition to, and the operation of, EMU. To this end, I evaluate the explanatory power of two approaches that make strongly contrasting assumptions about European integration: liberal intergovernmentalism and constructivism. The empirical evidence shows that a constructivist approach does a better job of explaining Germany's post-TEU policy on EMU than liberal intergovernmentalism. It has the tools to deal with what turns out to be crucial for understanding the policy in question: social identities. They shaped how central governmental decision-makers and the mass public lined up and acted on the issue of EMU. This finding is indicative of more general, theoretical weaknesses of liberal intergovernmentalism. The theory is overly rationalist and materialist. The EU is a unique institutional arrangement in which more than consequence-oriented action and material considerations matter. Therefore, constructivism, which is analytically strong precisely where liberal intergovernmentalism is weak, should be part of the standard toolbox of every scholar of the EU. However, the empirical findings of the article also suggest that constructivist research would benefit from paying attention to what it has ignored so far: mass identities.