Recent conflicts and crises in international relations have tested the ethical commitments of many cosmopolitans. However, this article argues that cosmopolitanism can be morally compelling and practically useful if it is conceived pragmatically as a set of ideals that guide interactions concerning cross-border problems. It argues that a will to believe in cosmopolitanism can be rationally justified by historical achievements and present tendencies in social conditions. Cosmopolitan beliefs are warranted, first, by demonstrating the empirical relevance of cosmopolitan ethics as a ‘living option’ in a new era of interaction and interdependence. Second, a pragmatic reorientation of cosmopolitan theory is conducted to widen the basis for identifying cosmopolitan action and permit a reconstruction of its ideals appropriate to today's pluralistic world. Finally, cosmopolitan ideals of equality, critical intelligence, and intercultural dialogue are developed as guides to addressing cross-border problems, drawing on the issue of climate change to illustrate how they become operative. A pragmatic faith in these ideals is thus justified by empirical hypotheses concerning the historical tendencies and latent potentialities of human experience, rather than metaphysical premises attached to a supernatural force or universal Reason.