The Patriarchal Cathedral Church of St. George (Greek: Πατριαρχικός Ναός του Αγίου Γεωργίου; Turkish: Aya Yorgi Kilisesi) is the principal Eastern Orthodox cathedral located in Istanbul, the largest city in Turkey and, as Constantinople, capital of the Byzantine Empire until 1453, and of the Ottoman Empire until 1922.

[a] The church, dedicated to the Christian martyr Saint George, is the site of numerous important services, and is where the patriarch will consecrate the chrism (myron) on Holy and Great Thursday, when needed.

This, however, can be explained by the Islamic laws of the Ottoman Empire that governed the rights of dhimmis, which stipulate that all non-Islamic buildings must be smaller and humbler than corresponding Islamic buildings such as mosques: prior to the Ottoman conquest of Constantinople in 1453, the Patriarchal cathedral was Hagia Sophia (also known as the Cathedral of the Holy Wisdom).

The interior is divided into three aisles by colonnades, with the tall pews of ebony wood placed along the line of the columns.

In the holy bema, behind the altar, the synthrone (cathedra) is arranged in a semicircle along the curved wall of the apse, with seats for the Archpriests and a central higher throne of marble for the Patriarch.

Its most precious objects, saved from each successive fire, are the patriarchal throne, which is believed to date from the 5th century, and some rare mosaic icons and the relics of Saints Basil the Great, Gregory the Theologian and John Chrysostom.

Some of the bones of these two saints, which were looted from Constantinople by the Fourth Crusade in 1204, were returned to the Church of St George by Pope John Paul II in 2004.

[citation needed] Since the fall of the Ottomans and the rise of modern Turkish nationalism, most of the Greek Orthodox population of Istanbul was deported or forced to emigrate after a series of minor or major violent incidents like the Istanbul pogrom, leaving the Patriarch in the anomalous position of a leader without a flock, at least locally.