The term cosmopolitanism is derived from the Greek word used to denote a “citizen of the world” (kosmopolitês). This notion of world citizenship is derived from the Greek terms for “universe” and “polis,” which were understood as moral and legal order. The central libertarian claim that all human beings—indeed, all rational agents—have equal fundamental rights is rooted in the ancient tradition of cosmopolitan thought. (Another use of the term, which refers to a person of worldly or sophisticated tastes, is not directly relevant to its moral/political use; one could have parochial or unsophisticated tastes, but cosmopolitan political beliefs.)

Cosmopolitanism has deep roots in Western culture. About the year 420 B.C., the philosopher Democritus wrote, “To a wise man, the whole earth is open; for the native land of a good soul is the whole earth.” According to the philosopher Diogenes Laertius, the following story was told of Diogenes the Cynic: “The question was put to him what countryman he was, and he replied, not ‘Citizen of Sinope,’ but ‘Citizen of the world’ (kosmopolitês).” The cosmopolitan idea was later articulated by such influential figures in the Roman world as Cicero, who in his De Officiis criticized those “who say that account should be taken of other citizens, but deny it in the case of foreigners; such men tear apart the common fellowship of the human race.” A number of later Stoic figures underscored the importance of living in accordance with “nature” and therefore not merely in accordance with the conventions of this or that city or country.

The idea of a universal moral order and of a higher law by which all human actions might be judged was poetically expressed in the Sermon on the Mount:

“You have heard that it was said, “You shall love your neighbor and hate your enemy.” But I say to you, Love your enemies and pray for those who persecute you, so that you may be sons of your Father who is in heaven; for he makes his sun rise on the evil and on the good, and sends rain on the just and on the unjust.”

This passage was repeatedly cited in arguments for universal standards of justice, notably by the lawyer-pope Innocent IV about the year 1250 in a legal opinion governing the wars with Islam. Innocent IV defended the rights of non-Christians on the grounds that

“lordship, possession and jurisdiction can belong to infidels licitly and without sin, for these things were not made only for the faithful but for every rational creature as has been said. For he makes his sun to rise on the just and the wicked and he feeds the birds of the air. Accordingly we say that it is not licit for the pope or the faithful to take away from infidels their belongings or their jurisdictions because they possess them without sin.”

As the notion of human rights developed throughout the medieval period, it too drew on the cosmopolitan tradition. Thus, in his arguments supporting the equal status of the American Indians, Bartolomé de las Casas, the Spanish Bishop of Chiapa, concluded his great defense of the Indians in 1552 by maintaining that “the Indians are our brothers, and Christ has given his life for them. Why, then, do we persecute them with such inhuman savagery when they do not deserve such treatment? The past, because it cannot be undone, must be attributed to our weakness, provided that what has been taken unjustly is restored.” That speech (and the book based on it) influenced all later discussions of human rights and set the stage for the emergence of libertarianism in full form, notably among the Levellers in England, who campaigned for universal human rights, including the freedom to trade and travel.

Cosmopolitanism has been closely connected with the mutual enrichment of cultures that came with increasing contact as opportunities for trade and travel expanded, a freedom that had long been a central libertarian demand. Joseph Addison, writing in The Spectator, famously illustrated a cosmopolitan attitude in his description of his visit to the Royal Exchange of London in 1711:

“Sometimes I am justled among a Body of Americans; sometimes I am lost in a Crowd of Jews, and sometimes in a Group of Dutch-Men. I am a Dane, a Swede, or Frenchman at different times, or fancy myself like the old Philosopher, who upon being asked what country-man he was, replied that he was a Citizen of the World.”

The theme was taken up again in the 20th century by such classical liberal figures as Ludwig von Mises, who wrote in Liberalism that, “for the liberal, the world does not end at the borders of the state. In his eyes, whatever significance national boundaries have is only incidental and subordinate. His political thinking encompasses the whole of mankind.”

Libertarian thinkers have often been rebuked by nationalists for their cosmopolitanism. Max Hildebert Boehm, in his influential discussion of cosmopolitanism, asserted that, “by standing, or aiming to stand, in immediate communion with all men, an individual easily avoids the risks and sacrifices which in view of the perpetual conflicts between all particularistic groups beset a social life based on narrower solidarities.” Boehm concluded that “it often exists among persons whom fortune has relieved from the immediate struggle for existence and from pressing social responsibility and who can afford to indulge their fads and enthusiasms.” The contemporary British philosopher David Miller, an articulate champion of both nationalism and socialism, dismisses cosmopolitans who hold that people “should regard their nationality merely as a historic accident, an identity to be sloughed off in favor of humanity at large.” Miller argues that anticosmopolitan nationalism is a necessary condition for the creation of socialism. Cosmopolitanism, according to Boehm, Miller, and other critics of libertarianism, undermines social justice.

Critics of libertarianism also assert that cosmopolitanism (often referred to as globalization) threatens cultural and, ultimately, personal identity. Communitarians such as Michael Sandel have argued that one’s identity rests on constitutive understandings that comprehend a wider subject than the individual alone. Sandel argues on epistemic grounds that the relevant unit of political analysis is not the individual, but some wider group. In the modern world, that is identified with the nation state, which, he alleges, exhaustively encompasses one’s identity. An alternative approach to understanding personal identity was articulated by the German legal historian Otto von Gierke, who noted that in the modern world no circle of association “encompasses the totality of a human being” inasmuch as the identity of each of us is formed by many overlapping commitments. The sociologist Georg Simmel characterized the modern liberal personality as emerging from an ever-expanding “intersection of social circles.” To be sure, there are differences among groups, including national groups, but modern identity is not formed by a concentric series of circles, with the nation-state forming the hard outer shell, but by an ever-expanding series of intersecting circles, many of which cut across national boundaries, as anyone with foreign friends or religious or other attachments that transcend national borders will attest.

Moreover, many critics charge that global freedom of trade and travel threatens to destroy the individuality of cultures and to rob people of their unique cultural identities. The debate is a complex one and has been joined by any number of writers who have argued that cultures tend to flourish when they are open to the influence from other cultures. Many also challenge the assumption of those who criticize globalization that there are pure cultures that are more authentic than others and that that purity is threatened by allowing people contact with other cultures. Living cultures, as opposed to dead museum exhibits, maintain their continuity by processing and adapting to influences from outside.

Cosmopolitanism, understood as recognition of a universal set of moral and political obligations and rights, has long been a core commitment of libertarian political thought. It remains, through the contemporary debates over globalization, a central source of controversy in political and social thought.