Defence date: 29 June 2015 ; Examining Board: Professor Rainer Bauböck, EUI (Supervisor); Professor Philippe Van Parijs, UC Louvain (Co-supervisor); Professor Hanspeter Kriesi, EUI; Professor Nadia Urbinati, Columbia University. ; This dissertation aims to arrive at a model of democratic legitimacy for the European Union. There is, however, a strain of thought pre-dominant in political theory since the nineteenth century that doubts the capacity of political systems constituted by multiple public spheres to have sustainable democratic systems. This view is referred to here as the lingua franca thesis on sustainable democratic systems (LFT). It states that, in the absence of a common language for political debate, democracy cannot function well in the long-term as citizens existing in distinctive public spheres will inevitably come to have diverging preferences that cannot be satisfactorily resolved by a collective democratic process. Poor quality democratic institutions, as well as acute demands to divide the political system (through devolution or secession) so that state and society become more congruent, are predicted by this thesis. To arrive at a model of democratic legitimacy for the EU, in light of the challenge presented by the LFT, three major steps are taken. Part One attempts to arrive at an account of democratic legitimacy as a realistic ideal for modern political systems. Understanding democracy as a system which strives to maximise citizens’ equal opportunities for control over the decisions to which they are subject, the maximisation of electoral and direct voting opportunities for citizens is recommended, subject to certain practical constraints. Importantly, democratically legitimate institutions are identified as having important external effects, which amount to more than just the peaceful resolution of conflict. Centripetal democracy is the idea that legitimate democratic institutions set in motion forms of citizen practice and representative behaviour that serve as powerful drivers of ...