A core feature of the emerging international governance of migration is the reliance on knowledge and science in elaborating policies. Yet how scientists and researchers can productively contribute to policy making is unclear. This is the result of knowledge uncertainty, the complexity of migration dynamics, and the unintended and counterproductive consequences policies. If research cannot say what “should be done,” it may tell policy makers what they definitively should not do. This article outlines some fundamental ethical norms that could serve this end, while warning that migration policies, like other policies, are often unable to live up even to the most minimal moral requirements.