Drawing on recent insights in the nationalism and citizenship regime literatures, this article develops a macrotheoretical framework for understanding cross-national variations in tolerance of ethnic minorities. Specifically, it tests the hypothesis that the degree to which the dominant ethnic tradition or culture is institutionalized in the laws and policies of a nation-state affects citizen tolerance of ethnic minorities. Employing a multilevel regression model, it systematically tests the framework, as well as competing individual and country-level explanations, for all member states of the European Union in 1997. Results confirm a strong relationship between the laws governing the acquisition and expression of citizenship, that is, citizenship regime type, and individual tolerance judgments. Moreover, citizenship regime type has a strong mediating effect on three individual-level variables previously shown to predict tolerance: ingroup national identity, political ideology, and satisfaction with democracy.