The separation of church and state is a philosophical and jurisprudential concept for defining political distance in the relationship between religious organizations and the state. Conceptually, the term refers to the creation of a secular state (with or without legally explicit church-state separation) and to disestablishment, the changing of an existing, formal relationship between the church and the state. Although the concept is older, the exact phrase "separation of church and state" is derived from "wall of separation between church and state", a term coined by Thomas Jefferson. The concept was promoted by Enlightenment philosophers such as John Locke.

In a society, the degree of political separation between the church and the civil state is determined by the legal structures and prevalent legal views that define the proper relationship between organized religion and the state. The arm's length principle proposes a relationship wherein the two political entities interact as organizations each independent of the authority of the other. The strict application of the secular principle of laïcité is used in France, while secular societies such as Denmark and England maintain a form of constitutional recognition of an official state religion.

The philosophy of the separation of the church from the civil state parallels the philosophies of secularism, disestablishmentarianism, religious liberty, and religious pluralism. By way of these philosophies, the European states assumed some of the social roles of the church and the welfare state, a social shift that produced a culturally secular population and public sphere. In practice, church–state separation varies from total separation, mandated by the country's political constitution, as in India and Singapore, to a state religion, as in the Maldives.