The Greek Orthodox Church of Jerusalem (Greek: Πατριαρχεῖον Ἱεροσολύμων Patriarcheîon Hierosolýmōn, Arabic كنيسة الروم الأرثوذكس في القدس), also known as the Greek Orthodox Patriarchate of Jerusalem, is a member of the Eastern Orthodox Communion. It is regarded by Orthodox Christians as the mother church of all of Christendom, because it was in Jerusalem that the Church was established on the day of Pentecost with the descent of the Holy Spirit on the disciples of Jesus Christ (). From Jerusalem the Gospel of Christ was spread to the world. This church is part of the universal Eastern Orthodox Church. It is also often called "Σιωνίτις Εκκλησία" (Greek: Sionitis Ecclesia, i.e. the "Church of Zion").
As Christianity spread, and the persecution of the Hebrews by Roman authorities in their homeland increased, causing the dispersion of many of the Hebrews and Christians from Jerusalem, the importance of the church of Jerusalem and its impact on the ongoing life of the whole Church diminished, though a remnant always remained in the city. Eusebius of Caesarea provides the names of an unbroken succession of thirty-six Bishops of Jerusalem up to the year 324. The first sixteen of these bishops were Jewish—from James the Brother of Jesus through Judas († 135)—the remainder were Gentiles.
By the time of the First Council of Nicaea in 325 the bishop of Aelia Capitolina (the name given to the Roman colony founded on the site of Jerusalem after Bar Kokhba's revolt), was not even the highest ranking in the province, being subject to the Metropolitan of Caesarea. However, the Council accorded the bishop a certain undefined precedence in its seventh canon. It gradually grew in prestige, and in a decree issued from the seventh session of the Council of Chalcedon in 451 it was recognized as possessing full Patriarchal status, ranked fifth after the Churches of Rome, Constantinople, Alexandria, and Antioch (see the article on Pentarchy). The Orthodox Church of Jerusalem remains the custodian of many of the holy sites in Jerusalem and environs, sometimes jointly with the Roman Catholic Church and the Oriental Churches (Egyptian and Ethiopian Coptics and Armenian Orthodox Christians).
Lately there has been criticism of the church leadership by some of the Palestinian faithful (known as Arab Orthodox) who accuse the Greek-speaking and largely Greek-born leadership of squandering their money and treating their Arabic-speaking members as second-class faithful. In 2005, a crisis of the patriarchy occurred when Patriarch Irenaios was stripped of his authority as patriarch by the Holy Synod of Jerusalem after he had allegedly leased church property in a very sensitive area of East Jerusalem to Israeli companies. The locum tenens (steward) until the election of a new patriarch was Metropolitan Cornelius of Petra.
The Palestinian faithful (Arab Orthodox) have expressed the desire to have local and or Palestinian leaders in the positions of authority in their respective districts, in contrast to the tradition (since Ottoman times) of the higher authority being made of ethnic Greeks. The Orthodox Church is sometimes compared unfavourably in this respect to the Melkite Greek Catholic Church, which has Arabic as its official and liturgical language.
The site remained buried beneath the pagan temple until Emperor Constantine the Great converted to Christianity in 312 AD.