Would unrestricted “economic” migration enhance the potential gains from free trade? With free migration, consumers' feasible sets become non-convex. Under standard assumptions, however, Walrasian equilibrium exists for a continuum of individuals with dispersed ability to afford each of a finite set of possible migration plans. Then familiar conditions ensuring potential Pareto gains from trade also ensure that free migration generates similar supplementary gains, relative to an arbitrary status quo. As with the gains from customs unions, however, wealth may have to be redistributed across international borders.