Gereja-gereja Ortodoks Yunani diturunkan dari gereja-gereja yang Para Rasul dirikan di Balkan dan Timur Tengah pada abad pertama Masehi,[11][12][13][14][15][16][17] dan mereka mengutamakan beberapa tradisi yang dipraktikan dalam Gereja kuno.[17] Gereja-gereja Ortodoks, tidak seperti Gereja Katolik, tidak memiliki kepala Uskup seperti Paus, dan memegang keyakinan bahwa Kristus adalah kepala Gereja. Namun, masing-masing dari mereka diperintah oleh suatu komite Uskup-Uskup, yang disebut Sinode Kudus, dengan satu Uskup utama yang diberi gelar kehormatan "yang pertama di antara yang setara" (bahasa Inggris: first among equals).
Gereja-Gereja Ortodoks Yunani disatukan dalam komuni dengan satu sama lain, serta dengan Gereja-Gereja Ortodoks Timur (seperti Gereja Ortodoks Rusia). Ortodoks Timur memegang doktrin umum dan bentuk peribadatan umum, dan mereka memandang diri mereka sendiri bukanlah sebagai Gereja-Gereja terpisah namun sebagai unit-unit administratif dari satu Gereja tunggal. Mereka dikenal karena tradisi ikonografi ekstensif mereka (lihat pula: seni rupa Bizantium), untuk menghormati Bunda Allah dan Santo/Santa, dan mereka mengadakan Liturgi Ilahi pada hari Minggu, yang merupakan pelayanan ibadat yang distandardisasikan yang bermula pada abad keempat Masehi. Liturgi Ilahi Gereja Ortodoks yang paling umum digunakan ditulis oleh Santo Yohanes Krisostomus (347–407 Masehi).
Terdapat juga beberapa penganut Kristen Ortodoks Yunani, yang bermula pada zaman Bizantium dan Kesultanan Utsmaniyah, yang merupakan leluhur pemakai bahasa Arab atau pemakai bahasa Yunani campuran dan tinggal di selatan Turki, Israel, Palestina, Irak, Suriah, Lebanon, Yordania, dan Mesir. Mereka menghadiri gereja yang mengadakan pelayanan mereka dalam bahasa Arab, bahasa umum dari sebagian besar para penganut Ortodoks Yunani di Syam, sementara pada waktu yang sama mengutamakan unsur-unsur dari tradisi kebudayaan Yunani Bizantium.
^The Flag Bulletin. 27. Flag Research Center. 1988. hlm. 105. Diarsipkan dari versi asli tanggal 2023-08-02. Diakses tanggal 2016-01-24. It is not surprising that all symbols of Mount Athos, especially the Byzantine double-eagle and the Holy Virgin, who is the patron of the Holy Mount, represent old Byzantine traditions. [...] The flag of Mount Athos (Fig. 1) is golden yellow bearing the black Byzantine double-headed eagle with an imperial crown. The eagle holds on its claws an orb of black with golden bands and a black...
^William G. Crampton (1990). The Complete Guide to Flags. Gallery Books. hlm. 57. ISBN978-0-8317-1605-9. Diarsipkan dari versi asli tanggal 2023-08-02. Diakses tanggal 2016-01-24. Greek Yellow with a 2-headed Orthodox black eagle (also for Mount Church Athos)
^Demetrios J. Constantelos, Understanding the Greek Orthodox Church, Holy Cross Orthodox Press 3rd edition (March 28, 2005)
^L. Rushton, Doves and magpies: village women in the Greek Orthodox Church Women's religious experience, Croom Helm, 1983
^Janet Saltzman Chafetz; Helen Rose Ebaugh (18 October 2000). Religion and the New Immigrants: Continuities and Adaptations in Immigrant Congregations. AltaMira Press. hlm. 155. ISBN978-0-7591-1712-9. Diarsipkan dari versi asli tanggal 2023-08-02. Diakses tanggal 2 September 2013. The distinctive characteristics of the Greek Orthodox Church are its sense of continuity with the ancient Church of Christ and the Apostles and its changelessness. The Orthodox church traces its existence, through the ordinatinon of Bishops. directly back to the Apostles and through them to Jesus.
^Sally Bruyneel; Alan G. Padgett (2003). Introducing Christianity. Orbis Books. hlm. 7. ISBN978-1-60833-134-5. Diarsipkan dari versi asli tanggal 2023-08-02. Diakses tanggal 2 September 2013. The Eastern Orthodox and thye Roman Catholic Churches are the oldest with roots going back to the earliest Christian groups.
^Robert L. Plummer (6 March 2012). Journeys of Faith: Evangelicalism, Eastern Orthodoxy, Catholicism and Anglicanism. Zondervan. hlm. 128. ISBN978-0-310-41671-5. Diarsipkan dari versi asli tanggal 2023-08-02. Diakses tanggal 2 September 2013. Catholicism holds that if a Church claims to be Christian, then it must be able to show that its leaders-its bishops and its presbyters (or priests)- are successors of the apostles. That is why the Catholic Church accepts Eastern Orthodox ordinations and sacraments as valid, even though Eastern Orthodoxy is not in full communion with Rome.
^William A. Dyrness; Veli-Matti Kärkkäinen (25 September 2009). Global Dictionary of Theology: A Resource for the Worldwide Church. InterVarsity Press. hlm. 244. ISBN978-0-8308-7811-6. Diarsipkan dari versi asli tanggal 2023-08-02. Diakses tanggal 2 September 2013. This connection is apparent through the historical succession of bishops of churches in a particular geographic locale and by fidelity to the teachings of the apostles (cf. Acts 2:42) and life as it developed in the patristic tradition and was articulated by the seven ecumenical councils.
^Heidi Campbell (22 March 2010). When Religion Meets New Media. Routledge. hlm. 13. ISBN978-0-203-69537-1. Diarsipkan dari versi asli tanggal 2023-08-02. Diakses tanggal 2 September 2013. There are three branches within Christianity: Catholic, Eastern Orthodox, and Protestant. ... The Christian church draws its lineage and roots from the time of Jesus Christ and the apostles in CE 25–30 and the birth of the Church at Pentecost in ...
^ abWendy Doniger (January 1999). Merriam-Webster's Encyclopedia of World Religions. Merriam-Webster. hlm. 309. ISBN978-0-87779-044-0. Diarsipkan dari versi asli tanggal 2023-08-02. Diakses tanggal 2 September 2013. EASTERN ORTHODOXY, one of the major branches of CHRISTIANITY, characterized by its continuity with the apostolic church, its liturgy, and its territorial churches.
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Fortesque, Adrian. The Orthodox Eastern Church (1929)
Hussey, Joan Mervyn. The orthodox church in the Byzantine empire (Oxford University Press, 2010) onlineDiarsipkan 2020-08-01 di Wayback Machine.
Kephala, Euphrosyne. The Church of the Greek People Past and Present (1930)
Latourette, Kenneth Scott. ' Christianity in a Revolutionary Age, II: The Nineteenth Century in Europe: The Protestant and Eastern Churches. (1959) 2: 479-484; Christianity in a Revolutionary Age, IV: The Twentieth Century in Europe: The Roman Catholic, Protestant, and Eastern Churches (1958)
McGuckin, John Anthony (ed.). The Encyclopedia of Eastern Orthodox Christianity. 2 vols. (Wiley-Blackwell, 2011).