The issue of international migration raises distinctive normative challenges for liberal democratic states, which regard certain rights and liberties as fundamental and have institutionalized them through constitutions. Most migrants want little more than to make better lives for themselves. If people wish to migrate across borders, why shouldn’t they be able to? States exercise power over borders, but what, if anything, justifies this power? If states are justified in excluding some and accepting others, what should be their criteria of selection? This chapter provides an overview of the leading normative positions on migration. It considers two main positions: arguments for open borders and arguments for state sovereignty. It then makes the case for a middle-ground position of qualified state sovereignty, “controlled borders and open doors.” The final section discusses two challenges to liberal constitutionalism posed by migration: what is owed to refugees outside a state’s borders and unauthorized migrants inside a state’s borders.