Why do some countries tolerate dual citizenship while others do not? The answer concerns the interaction between regime type variation and international migration. Democracies with a relatively large migrant stock are more likely to tolerate dual citizenship than democracies with a low migrant stock. Meanwhile, democracies with relatively high emigration rates for the highly educated population are more likely to tolerate dual citizenship than democracies with low emigration rates of the highly educated. In authoritarian states, the opposite is the case: emigration of the highly educated and immigration both reduce the likelihood of dual citizenship toleration. These claims are supported by the evidence from a large n examination of contemporary cross-national data. Understanding dual citizenship helps us address larger questions about the significance of democracy and the nature and scope of nation states.