With republican theory emerging as a form of scholarly inquiry on Europe’s puzzling transformations, a variety of civic conceptions of the European Union (EU) bring into focus the uses of normative theory. This paper, drawing from a rich intellectual tradition, argues that a challenge central to EU constitutionalism is to utilize Europe’s republican tradition for its emerging polity. But we also need a new way of theorizing European diversity, as the latter transcends national differences by embracing a variety of cultural and spatial dimensions. But how are we to combine a robust (republican) grounding for constitutionalism and a celebratory affirmation of differences? We suggest that, by tackling the question of democracy in the EU from a liberal republican angle that endorses a new form of civic polyculturalism, one can assign meaning to Europe’s envisaged transformation into a res publica composita. The theoretical challenge is thus set: to go beyond what is evident in Europe’s novel experimentations with democracy so as to embrace latent but crucial potentialities.