Within the immigration debate, libertarians have typically come down in favor of open borders by defending two main ideas: (i) individuals have a right to free movement; and (ii) immigration restrictions are economically inefficient, so that lifting them can make everyone better off. This entry describes the rationale for open borders from a libertarian perspective (in part by analogy to the debate around minimum wage laws). Three main objections within the immigration literature are then discussed: (i) the view that states may restrict immigration to protect the interests (e.g., jobs) of their domestic needy; (ii) the claim that restrictions are justified as a means of preserving culture; and (iii) the influential argument that the right to freedom of association entails a right to exclude. These arguments are well-known, and I describe some of the compelling responses to be found in the recent literature. The essay then turns to more neglected critiques. The first concerns how liberal regimes should think about immigration from countries where the dominant norms are illiberal. The second examines the idea that political and economic institutions are sensitive to immigration policy, especially in the long run. Both of these critiques approach the topic from a non-ideal theory perspective, emphasizing the “public choice” dimensions of immigration policy. The chapter closes by suggesting that this form of critique is especially important for open-borders libertarians to respond to given their general commitments to non-ideal, non-romantic theorizing in the context of government institutions and policy.