A state religion (also called an established religion or official religion) is a religious body or creed officially endorsed by the state. A state with an official religion, while not secular, is not necessarily a theocracy, a country whose rulers have both secular and spiritual authority. State religions are official or government-sanctioned establishments of a religion, but the state does not need be under the control of the religion (as in a theocracy) nor is the state-sanctioned religion necessarily under the control of the state.
Official religions have been known throughout human history in almost all types of cultures, reaching into the Ancient Near East and prehistory. The relation of religious cult and the state was discussed by Varro, under the term of theologia civilis ("civic theology"). The first state-sponsored Christian church was the Armenian Apostolic Church, established in 301 CE. In Christianity, as the term church is typically applied to a Christian place of worship or organisations incorporating such ones, the term state church is associated with Christianity as sanctioned by the government, historically the state church of the Roman Empire in the last centuries of the Empire's existence, and is sometimes used to denote a specific modern national branch of Christianity. Closely related to state churches are ecclesiae, which are similar but carry a more minor connotation.
In the Middle East, many states with primarily Islamic population have Islam as their state religion, though the degree of religious restrictions on the citizen's everyday life varies by country. Rulers of Saudi Arabia use both secular and religious power, while Iran's secular presidents are supposed to follow the decisions of religious authorities since the revolution of 1979. Turkey, which also has a primarily Muslim population, became a secular country after Atatürk's Reforms, although unlike the Russian Revolution of the same time period, it did not result in the adoption of state atheism.
The degree to which an official national religion is imposed upon citizens by the state in contemporary society varies considerably; from high as in Saudi Arabia to minimal or none at all as in Denmark, England, Iceland, and Greece.
The elevation of Christianity to a state religion following the conversion of the Emperor Constantine, resulted in the imposition of faith by secular government and resulted in the abuses perpetrated by the Roman Catholic Church, eventually opposed through the processes of the Reformation and the rise of Protestant and secular forces and resulting in the separation of church and state. In many countries legislation continues to favour the historically dominant religion. In Belgium, for example, non-Catholic churches have been restricted architecturally in their visibility from the street.