  The word ‘cosmopolitan’, which derives from the Greek word kosmopolitēs (‘citizen of the world’), has been used to describe a wide variety of important views in moral and socio-political philosophy. The nebulous core shared by all cosmopolitan views is the idea that all human beings, regardless of their political affiliation, are (or can and should be) citizens in a single community. Different versions of cosmopolitanism envision this community in different ways, some focusing on political institutions, others on moral norms or relationships, and still others focusing on shared markets or forms of cultural expression. In most versions of cosmopolitanism, the universal community of world citizens functions as a positive ideal to be cultivated, but a few versions exist in which it serves primarily as a ground for denying the existence of special obligations to local forms of political organizations. Versions of cosmopolitanism also vary depending on the notion of citizenship they employ, including whether they use the notion of ‘world citizenship’ literally or metaphorically. The philosophical interest in cosmopolitanism lies in its challenge to commonly recognized attachments to fellow-citizens, the local state, parochially shared cultures, and the like.