A List of Orthodox Ecumenical Councils
From the Notes of Lay-Brother Michael

* I. First Council of Nicea, (325); repudiated Arianism, adopted the Nicene Creed.

* II. First Council of Constantinople, (381); revised the Nicene Creed into the present form used in the Eastern and Oriental Orthodox churches.

* III. Council of Ephesus, (431); repudiated Nestorianism, proclaimed the Virgin Mary as the Mother of God (Greek, Theotokos).

* IV. Council of Chalcedon, (451); repudiated the Eutychian doctrine of Monophysitism, described and delineated the two natures of Christ, human and divine; adopted the Chalcedonian Creed. This and all following councils are not recognized by Oriental Orthodox Communion (Eastern Syriacs).

* V. Second Council of Constantinople, (553); reaffirmed decisions and doctrines explicated by previous Councils, condemned new Arian, Nestorian, and Monophysite writings.

* VI. Third Council of Constantinople, (680-681); repudiated Monothelitism, affirmed that Christ had both human and Divine wills.

* * Quinisext/Penthekte Council (= Fifth and Sixth) or Council of Trullo, (692); mostly an administrative council that raised some local canons to ecumenical status and established principles of clerical discipline. It is not considered to be a full-fledged council in its own right because it did not determine matters of doctrine. This council is accepted by the Orthodox Church as a part of the Sixth Ecumenical Council, but that is rejected by Roman Catholics.

* VII. Second Council of Nicaea, (787); restoration of the veneration of icons and the end of the first iconoclasm.

***The next two are regarded as ecumenical by some in the Orthodox Church but not by other Orthodox Christians, who instead consider them to be important local councils.

* VIII. Fourth Council of Constantinople, (879-880); restored St. Photius the Great to his see in Constantinople and anathematized any who altered the Nicene-Constantinopolitan Creed, abrogating the decrees of the Robber Council of 869-870. This council was at first accepted as ecumenical by the West but later (in the 11th century) repudiated it in favor of the Robber Council which had deposed Photius.

IX. Fifth Council of Constantinople, (1341-1351); affirmed hesychastic theology according to St. Gregory Palamas and condemned the Westernized philosopher Barlaam of Calabria.