Recent scholarship has emphasized the importance of concepts rooted in social identity for understanding citizen attitudes towards the European Union (EU). This article builds upon prior research by developing an argument that authoritarians are more likely to oppose the EU and to hold exclusionary social identity attitudes. Authoritarians, who have a predisposition towards order and conformity, are likely to oppose the EU as it threatens the established social and political order of the sovereign state and the dominant national culture. In addition, authoritarians are more likely to express exclusionary social identities. Analysis of survey data finds support for these claims and demonstrates that authoritarianism decreases support for the EU directly and indirectly through various indicators of social identity attitudes.