This research questions the seemingly ossified premise that states have an absolute discretion to control international migration. Applying Max Weber's theories of legitimacy, it determines that while states have certain traditionally legitimate functions, migration control, as distinct from the determination of citizenship, is not one such function. Measures of migration control must thus be justified on a rational-legal basis, that is, on a minimal evidential basis. Acknowledging the many obstacles states face in carrying out this legitimising exercise, it is suggested that a supranational...