In the political domain, integration refers to the sociological process on which the social cohesion of a civic community depends. As such, integration has a functional dimension—i.e. the coordination of individual actions—as well as a normative component—i.e. the principles, values and culture that ground and motivate the citizens’ sense of belonging. Migration raises specific issues with regard to integration, related both to the impact of immigration on social cohesion and to the political conditions of migrants’ access to citizenship. In political theory, the connection between migration and integration therefore focuses on the fair terms of integration for immigrants in liberal democracies. Section 1 of this paper specifies these issues and places them in their intellectual background, going back to the nineteenth century’s philosophical distinction between the “ethnic vs. civic” conception of the modern nation and to the twentieth century’s sociological works on nations, nationalisms and interethnic relations. Section 2 analyses three prevailing normative models of integration in political theory: integration as assimilation, as multicultural recognition or as national civic inclusion. Section 3 questions the theoretical limits of such models that are focused on long-term immigrants and their possible naturalisation; it calls for future research that reassesses the fair terms of integration by addressing more precisely the changing features of international migration, the emergence of transnational citizenship and the issue of refugees.