EuroPolis explores the forms of democratic deficit that directly affecting EU citizens. We test the hypothesis that citizen involvement in inclusive, informed, and thoughtful deliberation about the EU increases access to politically relevant information, citizens’ political engagement in EU public affairs, perceptions of the legitimacy of EU institutions, a sense of belonging to the EU, and voter turnout in EU parliamentary elections. We draw our hypothesis from the theory of deliberative democracy that suggests that democratic legitimacy rests on open deliberation, and prescribes that citizens should become involved in politics. EuroPolis intends to assess the political outcomes of deliberative democratic practices by experimenting what would happen if EU citizens became substantially more informed about EU institutional arrangements, decision-making processes, and policy issues, as well as more aware of the policy preferences of other EU citizens. Would this make them evaluate EU policy alternatives differently from the way they would with limited information? Would their policy preferences change? Would their electoral choices be more aligned with their policy preferences and be more or less likely to vote in second-order elections? Would their electoral choices change? And if EU citizens had equal opportunity to engage in a thoughtful dialogue with citizens of other EU nationalities to discuss what they expect from their Union, would they identify the interests and problems they share with other EU citizens? Would they develop stronger bonds with fellow EU citizens and feel part of the Union they formally belong to? Would there be an increase in civic engagement? EuroPolis will seek to answer these questions through a carefully designed experiment that will assess how political and social attitudes toward EU issues change as a result of exposure to politically relevant information, and what difference this makes for political participation and voter turnout.