This article discusses the normative implications of the European integration process by addressing the question of the legitimacy deficit in the EU and its member states. It starts from an analysis of legitimacy as implying a distinction between `polity' and `regime', each of which has an `internal' and an `external' dimension relating respectively to the subjective perceptions of citizens and to more objective- and universalist-oriented criteria. Standard accounts of the integration process and the constitutionalisation of the EU have overlooked the (...) complex ways in which polity- and regime-building interact. They have also emphasized the external legitimacy of the EU while neglecting the internal dimension. Both descriptively and prescriptively, the EU lies in between the interpretations offered by neofunctionalist or intergovernmental realists and federal idealists. The `internal' norms channelled through the EU's `regime' have helped form the economic interests appealed to by the former, but in rather different ways to that assumed by the latter. The result has been a polycentric `polity' with a multi-level `regime'. Consequently, we reject having either an EU written constitution that goes beyond the treaties or a federal legislature, advocating instead the `republican' model of a `mixed commonwealth'. (shrink)