The secession of the North African churches over their Donatism was a minor and relatively short-lived schism in the catholic and apostolic churches. A more serious and thus-far permanent schism, however, was the defection of the Coptic Orthodox and the Armenian Apostolic Church (referred to as the “Oriental Orthodox” churches) after the Ecumenical Council of Chalcedon, which condemned monophysitism.

Considered by the churches more tragic, because of the hundreds of millions of believers it involves, is the Great Schism between the Latin churches (Roman Catholic) under the bishop of Rome, and the Greek churches (Eastern Orthodox), whose ecumenical patriarch (archbishop) is in Constantinople (now officially Istanbul). Eastern Orthodoxy includes the Greek and Russian Orthodox, and many other autonomous and national churches like the Romanian, Ukrainian, Serbian, Antiochian, Bulgarian, and Carpatho-Russian Orthodox.

The Great Schism culminated with the serving of excommunication letters between the pope of Rome and the ecumenical patriarch in 1054, and has been exacerbated by doctrinal disputes such as the filioque (Roman Catholic doctrine that states the Holy Ghost proceeds from the Son as well as from the Father) and papal authority. Most historians say that it had been in the making for centuries, from the time the Roman Empire was divided, and most educated people on both sides no longer spoke both official languages.

Since the Schism, the Latin Crusaders' sacking of Constantinople in 1204 and certain innovations in Catholic dogma have exacerbated the conflict. In the other direction, Pope John Paul II apologized for the atrocity of the Crusaders, and both sides have rescinded their excommunications of the other. The main doctrinal issues between the communions now are papal authority, the filioque, the immaculate conception of Mary, purgatory, and indulgences.