In general, a world citizen is a person who places global citizenship above any nationalistic or local identities and relationships. An early expression of this value is found in Diogenes of Sinope (c. 412 B.C.; mentioned above), a Cynic philosopher in Ancient Greece. Of Diogenes it is said: "Asked where he came from, he answered: 'I am a citizen of the world (kosmopolitês)'". This was a ground-breaking concept because the broadest basis of social identity in Greece at that time was either the individual city-state or the Greeks (Hellenes) as a group. The Tamil poet Kaniyan Poongundran wrote in Purananuru, "To us all towns are one, all men our kin." In later years, political philosopher Thomas Paine would declare, "my country is the world, and my religion is to do good." Today, the increase in worldwide globalization has led to the formation of a "world citizen" social movement under a proposed world government. In a non-political definition, it has been suggested that a world citizen may provide value to society by using knowledge acquired across cultural contexts.[ Many people also consider themselves world citizens, as they feel at home wherever they may go.

Albert Einstein described himself as a world citizen and supported the idea throughout his life. famously saying "Nationalism is an infantile disease. It is the measles of mankind. World citizenship has been promoted by distinguished people including Garry Davis, who lived for 60 years as a citizen of no nation, only the world. Davis founded the World Service Authority in Washington, DC, which sells World Passports, a fantasy passport to world citizens. In 1956 Hugh J. Schonfield founded the Commonwealth of World Citizens, later known by its Esperanto name "Mondcivitana Respubliko", which also issued a world passport; it declined after the 1980s.

The Bahá'í faith promotes the concept through its founder's proclamation (in the late 19th century) that "The Earth is but one country, and mankind its citizens." As a term defined by the Bahá'í International Community in a concept paper shared at the 1st session of the United Nations Commission on Sustainable Development, New York, U.S.A. on 14–25 June 1993. "World citizenship begins with an acceptance of the oneness of the human family and the interconnectedness of the nations of 'the earth, our home.' While it encourages a sane and legitimate patriotism, it also insists upon a wider loyalty, a love of humanity as a whole. It does not, however, imply abandonment of legitimate loyalties, the suppression of cultural diversity, the abolition of national autonomy, nor the imposition of uniformity. Its hallmark is 'unity in diversity.' World citizenship encompasses the principles of social and economic justice, both within and between nations; non-adversarial decision making at all levels of society; equality of the sexes; racial, ethnic, national and religious harmony; and the willingness to sacrifice for the common good. Other facets of world citizenship—including the promotion of human honour and dignity, understanding, amity, co-operation, trustworthiness, compassion and the desire to serve—can be deduced from those already mentioned.