Through the centuries the Catholic Church has encountered false teaching or practices that were contradictory to its basic doctrines and beliefs. Church Councils were called to counter these issues and to clarify the basic teaching of the Church. The Pope in union with the bishops of the Church have maintained a consistency of teaching in doctrine and morals in these councils.

Ecumenical Councils are those to which the bishops, and others entitled to vote, are convoked from the whole world ( oikoumene ) under the presidency of the pope or his legates, and the decrees of which, having received papal confirmation, bind all Christians.

First Ecumenical Council: Nicaea I (325). To this council we owe The Nicene Creed , defining against Arius the true Divinity of the Son of God, and the fixing of the date for keeping Easter.

Second Ecumenical Council: Constantinople I (381). It was directed against the followers of Macedonius, who denied the Divinity of the Holy Spirit. To the above-mentioned Nicene Creed it added the clauses referring to the Holy Spirit.

Third Ecumenical Council: Ephesus (431). It defined the true personal unity of Christ, declared Mary the Mother of God ( theotokos ) against Nestorius, Bishop of Constantinople, and renewed the condemnation of Pelagius.

Fourth Ecumenical Council: Chalcedon (451). It defined the two natures (Divine and human) in Christ against Eutyches, who was excommunicated.

Fifth Ecumenical Council: Constantinople II (553). It condemned the errors of Origen and certain writings ( The Three Chapters ) of Theodoret, of Theodore, Bishop of Mopsuestia and of Ibas, Bishop of Edessa ; it further confirmed the first four general councils, especially that of Chalcedon whose authority was contested by some heretics.

Sixth Ecumenical Council: Constantinople III (680-681). It put an end to Monothelitism by defining two wills in Christ, the Divine and the human, as two distinct principles of operation. It anathematized Sergius, Pyrrhus, Paul, Macarius, and all their followers.

Seventh Ecumenical Council: Nicaea II (787). It regulated the veneration of holy images.

Eighth Ecumenical Council: Constantinople IV (869). It consigned to the flames the Acts of an irregular council ( conciliabulum ) brought together by Photius against Pope Nicholas and Ignatius the legitimate Patriarch of Constantinople; it condemned Photius who had unlawfully seized the patriarchal dignity. The Photian Schism, however, triumphed in the Greek Church, and no other general council took place in the East.

Ninth Ecumenical Council: Lateran I (1123). It abolished the right claimed by lay princes, of investiture with ring and crosier to ecclesiastical benefices and dealt with church discipline and the recovery of the Holy Land from the infidels.

Tenth Ecumenical Council: Lateran II (1139). Its object was to put an end to the errors of Arnold of Brescia.

Eleventh Ecumenical Council: Lateran III (1179). It condemned the Albigenses and Waldenses and issued numerous decrees for the reformation of morals.

Twelfth Ecumenical Council: Lateran IV (1215). It issued an enlarged creed against the Albigenses, condemned the Trinitarian errors of Abbot Joachim, and published 70 important reformatory decrees. This is the most important council of the Middle Ages, and it marks the culminating point of ecclesiastical life and papal power.

Thirteenth Ecumenical Council: Lyons I (1245). It excommunicated and deposed Emperor Frederick II and directed a new crusade, under the command of St. Louis, against the Saracens and Mongols.

Fourteenth Ecumenical Council: Lyons II (1274). It effected a temporary reunion of the Greek Church with Rome. The word filioque was added to the symbol of Constantinople and means were sought for recovering Palestine from the Turks. It also laid down the rules for papal elections.

Fifteenth Ecumenical Council: Vienne (1311-1313). The synod dealt with the crimes and errors imputed to the Knights Templars, the Fraticelli, the Beghards, and the Beguines, with projects of a new crusade, the reformation of the clergy, and the teaching of Oriental languages in the universities.

Sixteenth Ecumenical Council: Constance (1414-1418). The Council of Constance was held during the great Schism of the West, with the object of ending the divisions in the Church. It became legitimate only when Gregory XI had formally convoked it. Owing to this circumstance it succeeded in putting an end to the schism by the election of Pope Martin V, which the Council of Pisa (1403) had failed to accomplish on account of its illegality. The rightful pope confirmed the former decrees of the synod against Wyclif and Hus. This council is thus ecumenical only in its last sessions (XLII-XLV inclusive) and with respect to the decrees of earlier sessions approved by Martin V.

Seventeenth Ecumenical Council: Basle/Ferrara/Florence (1431-1439). The Council of Basle met first in that town, Eugene IV being pope, and Sigismund Emperor of the Holy Roman Empire. Its object was the religious pacification of Bohemia. Quarrels with the pope having arisen, the council was transferred first to Ferrara (1438), then to Florence (1439), where a short-lived union with the Greek Church was effected, the Greeks accepting the council's definition of controverted points. The Council of Basle is only ecumenical till the end of the twenty-fifth session, and of its decrees Eugene IV approved only such as dealt with the extirpation of heresy, the peace of Christendom, and the reform of the Church, and which at the same time did not derogate from the rights of the Holy See. (See also the Council of Florence.)

Eighteenth Ecumenical Council: Lateran V (1512-1517). Its decrees are chiefly disciplinary. A new crusade against the Turks was also planned, but came to naught, owing to the religious upheaval in Germany caused by Luther.

Nineteenth Ecumenical Council: Trent (1545-1563). It was convoked to examine and condemn the errors promulgated by Luther and other Reformers, and to reform the discipline of the Church. Of all councils it lasted longest, issued the largest number of dogmatic and reformatory decrees, and produced the most beneficial results.

Twentieth Ecumenical Council: Vatican I (1869-1870). Besides important canons relating to the Faith and the constitution of the Church, the council decreed the infallibility of the pope when speaking ex cathedra , i.e. when as shepherd and teacher of all Christians, he defines a doctrine concerning faith or morals to be held by the whole Church.

Twenty-first Ecumenical Council: Vatican II (1962-1965). It was convened by Pope John XXIII to spiritually renew the church and examine its position in the modern world. Up to this point in the Twentieth Century the Church was living under the structure and rules of the Council of Trent. The seminaries and convents were bursting with record crops of new priests and nuns. The Church appeared to be both healthy and vibrant in Europe, the United States, and throughout the world. The missions were producing record numbers of converts. Pope Paul VI took over the chair of St. Peter in 1963, reconvening the Council. Soon after the Council ended, the masterful Documents of Vatican II was published. Poorly implemented in many countries, they became an excuse for widespread experimentation with the liturgy of the Mass and for reworking the constitutions and regulations of the religious orders. Less than ten years later began an enormous exodus from the priesthood and religious life. See also: Vatican II questioned.