Citizens’ attitudes toward the European Union (EU) are important, changing, and multidimensional. Still comparative studies of the dimensional structure of EU-attitudes are virtually absent. Using an extensive battery of EU attitude-items in a 21-country study, we test the dimensional structure of EU attitudes cross-nationally and assess the variation in this dimensional structure. We find (1) that EU attitudes are indeed multidimensional, also comparatively, (2) that the structure varies, but (3) that the structure is widely applicable especially when the EU is more salient in a country. Surprisingly, the attitudinal structure is not more pronounced in long-standing member states, and the structure is most outspoken in countries experiencing a change in migration. The implications for the study of EU attitudes are discussed.