The model for all ecumenical councils is the Council of Jerusalem, recalled in the Acts of the Apostles, chapter 15. However, it is not generally listed as one of the 20 ecumenical councils of Church history.
Ecumenical (from the Greek word oikoumene) means worldwide, and the first one was called by the Emperor of the known world, Constantine I.
1. First Council of Nicea in 325 defined the heresy of Arianism.
2. First Council of Constantinople in 381 again repudiated Arianism.
3. Council of Ephesus in 431 declared Mary as "God carrier" or Theotokos.
4. Council of Chalcedon in 451 made more explicit that Jesus' divine and human natures were united in a single being.
5. Second Council of Constantinople in 553 condemned Origen of Alexandria, the first great Scripture scholar of Christianity, for some odd ideas he had about the transmigration of souls.
6. Third Council of Constantinople in 680-681 dealt with more threats to unity of Christ, specifically a theory that Jesus had two wills — one divine and one human — but one nature. Monothelitism was condemned as heresy.
7. Second Council of Nicea in 787 tried to stop people from going around smashing icons. Veneration of icons was defined as good and iconoclasm was condemned.
8. Fourth Council of Constantinople in 869-870 restored St. Ignatius to his throne as Patriarch of Constantinople.
9. First Lateran Council in 1123 excommunicated the Holy Roman Emperor Henry V and declared it heresy for kings, princes and even the Holy Roman Emperor to appoint bishops. This was known as the investure controversy and it went on for centuries. The council also tried to impose celibacy on secular priests.
10. Second Lateran Council in 1139 was another attempt to get kings out of the business of the Church, and also tried to reform the clergy, including another condemnation of marriage among priests.
11. Third Lateran Council in 1179 condemned the sale of sacraments and positions in the hierarchy (simony) and declared only cardinals could elect the pope.
12. Fourth Lateran Council in 1215 defined transubstantiation, a term that remained controversial at the Second Vatican Council.
13. First Council of Lyon in 1245 excommunicated and deposed Holy Roman Emperor Frederick II who had put Rome under siege. Pope Innocent IV also used the Council to strike an alliance with King Louis IX of France and launch the Seventh Crusade under the French king's command.
14. Second Council of Lyon in 1274 under Blessed Pope Gregory X tried to repair the Great Schism of 1054. However, Greek Orthodox bishops were condemned for attending the Council when they returned home.
15. Council of Vienna in 1311 to 1312 marked the end of the crusades. The Knights Templar lost their Church support and Franciscan Ramon Llull (Raymond Lully) convinced the Council fathers the only way to retake the Holy Land was to learn the languages — specifically Hebrew, Arabic and Greek.
16. Council of Constance in 1414 to 1418 had to solve the problem of three popes: Anti-pope John XXIII, Avignon Pope Benedict XIII and Pope Gregory XII had all been elected by some bishops in a situation known as the Western Schism of 1378 to 1417. The Council of Constance resolved the schism by declaring an ecumenical council is a higher authority even than the pope who convokes it and then installing Pope Martin V.
17. Council of Florence opened in 1431 in Basel with no bishops, moved to Ferrara, Florence and finally Lousanne. There were wars in Bohemia, a rising threat in the Ottoman Empire and plague. The council tried to assert the idea of conciliarity, that councils should be part of the normal governance of the Church, and it achieved a short-lived reconciliation with some Greek Orthodox bishops and the Armenian Church.
18. The Fifth Lateran Council, the last before the Reformation, from 1512 to 1517 amounted to a battle royal between the forces of conciliarism and Pope Julius II's convictions about papal authority. Master of the Dominican order Thomas Cajetan argued for absolute papal authority against University of Paris theologian Jacques Almain. The Council passed a decree backing Cajetan's position.
19. Council of Trent from 1559 to 1565 tried to answer the challenge of Martin Luther, but came along too late to reunite a divided Western Church. The council's doctrine of salvation, definitions of the sacraments and reforms to the liturgy defined Catholicism for 350 years. It initiated the Catechism of 1568, a new Roman Missal which defined the Tridentine Mass, issued a new edition of the Vulgate — the Bible in Latin — and pronounced a long series of anathemas. It also envisioned the seminary system in the hope of a better educated clergy and encouraged the Mass in local languages, a reform that had to wait for the Second Vatican Council.
20. First Vatican Council of 1869 to 1870 defined papal infallibility. Papal infalibility was then used in 1950 by Pope Pius XII to declare the Assumption of the Blessed Virgin Mary into Heaven a universally accepted dogma of the Church.
21. Second Vatican Council of 1962 to 1965 was convoked after the Second World War and during the Cold War by Blessed Pope John XXIII.