The paper discusses from a comparative perspective the specific form of intergovernmentalism institutionalized in the European Union (EU), in particular in the Economic and Monetary Union (EMU). On the basis of the distinction between federations by aggregation (federal unions) and federations by disaggregation (federal states), the paper investigates the different forms of influence that constituent states exercise on the federal decision-making process of the two types of federation, showing that intergovernmentalism in the EU does not fit either of the two models. Contrary to the federal unions, like the USA and Switzerland, in the EU the constituent states are represented by their governments. Constituent states are instead represented by their governments in federal states like Germany (and informally in Canada), but in none of them they play the domineering role as in the EMU. Indeed, EMU has emerged as a highly centralized and hierarchical union, where national governments operate in an accountability vacuum at the central level, that challenges basic principles of democratic legitimacy.
