Immigration is often discussed in the framework of political economy and security studies. When discussed in the context of national identity, immigration is invariably depicted as a “challenge” or an “obstacle” for a nation-state. However, I argue that the impact of immigration on nation-building is contingent upon state policies toward ethnic diversity, something I call an “ethnicity regime.” Depending on the ethnicity regime in place, immigration can be a resource and a key instrument in support of new nationalist projects. I argue that this may have already been the case in Russia since the end of the Cold War. In Russia, mass immigration is aiding Russia’s transformation from a multiethnic state to an assimilationist one.