Long-term immigrants often have the option but not the obligation to acquire citizenship in their state of residence. Contrary to the received wisdom, this article defends the idea of mandatory citizenship for immigrants. It suggests that the current asymmetry in the distribution of political obligations between native-born citizens and immigrants is unfair. It also argues that mandatory citizenship is required by the principle that those who persistently affect others should share a democratic setting. Finally, it claims that mandatory citizenship is more compatible with the ideal of democratic equality and more conducive to a stable society.