International borders concentrate opportunities in some societies while limiting them in others. Borders also prevent those in the less favored societies from gaining access to opportunities available in the more favored ones. Both distributive effects of borders are treated here within a comprehensive framework. I argue that each state should have broad discretion under international law to grant or deny entry to immigration seekers; but more favored countries that find themselves under immigration pressure should be legally obligated to fund development (...) assistance for countries that generate immigration pressure. Funding should be subject to conditions of fair and effective use in recipient countries, and should aim at a near-term target of immigration-pressure equilibrium. Equilibrium obtains between two countries when, given appropriate background circumstances, the same proportion of individuals in each manifests a preference to migrate to the other. If meeting the equilibrium target in the short term would be to the long-term disadvantage of the worst-off countries, then a Pareto-superior alternative target supersedes. It mandates development assistance at the level that yields the most favorable human development projections for the worstoff countries. An implementable set of institutions is described that can achieve the equilibrium goal in the long term without unduly sacrificing other important ends, including economic growth, political stability, cultural integrity, the political autonomy of distinct societies, and their proper accountability for policy choices. Key Words: global justice • immigration • borders • development • distributive justice • development assistance • equality • international law • cosmopolitanism. (shrink)