any of the five ecumenical councils of the Roman Catholic Church held in the Lateran Palace in Rome.

The first Lateran Council, the ninth ecumenical council (1123), was held during the reign of Pope Calixtus II; (Calixtus II) no acts or contemporary accounts survive. The council promulgated a number of canons (probably 22), many of which merely reiterated decrees of earlier councils. Much of the discussion was occupied with disciplinary or quasi-political decisions relating to the Investiture Controversy settled the previous year by the Concordat of Worms; simony was condemned, laymen were prohibited from disposing of church property, clerics in major orders were forbidden to marry, and uncanonical consecration of bishops was forbidden. There were no specific dogmatic decrees.

The second Lateran Council, the 10th ecumenical council (1139), was convoked by Pope Innocent II to condemn as schismatics the followers of Arnold of Brescia, a vigorous reformer and opponent of the temporal power of the pope, and to end the schism created by the election of Anacletus II (Anacletus (II)), a rival pope. Supported by St. Bernard of Clairvaux and later by Emperor Lothar II, Innocent was eventually acknowledged as the legitimate pope. Besides reaffirming previous conciliar decrees, the second Lateran Council declared invalid all marriages of those in major orders and of professed monks, canons, lay brothers, and nuns. The council repudiated the heresies of the 12th century concerning holy orders, matrimony, infant Baptism, and the Eucharist.

The third Lateran Council, the 11th ecumenical council, was convoked in 1179 by Pope Alexander III and attended by 291 bishops who studied the Peace of Venice (1177), by which the Holy Roman emperor, Frederick I Barbarossa, agreed to withdraw support from his antipope and to restore the church property he had seized. This council also established a two-thirds majority of the College of Cardinals as a requirement for papal election and stipulated that candidates for bishop must be 30 years old and of legitimate birth. The heretical Cathari (or Albigenses) were condemned, and Christians were authorized to take up arms against vagabond robbers. The council marked an important stage in the development of papal legislative authority.

The fourth Lateran Council, the 12th ecumenical council (1215), generally considered the greatest council before Trent, was years in preparation. Pope Innocent III desired the widest possible representation, and more than 400 bishops, 800 abbots and priors, envoys of many European kings, and personal representatives of Frederick II (confirmed by the council as emperor of the West) took part. The purpose of the council was twofold: reform of the church and the recovery of the Holy Land. Many of the conciliar decrees touching on church reform and organization remained in effect for centuries. The council ruled on such vexing problems as the use of church property, tithes, judicial procedures, and patriarchal precedence. It ordered Jews and Saracens to wear distinctive dress and obliged Catholics to make a yearly confession and to receive Communion during the Easter season. The council sanctioned the word transubstantiation as a correct expression of eucharistic doctrine. The teachings of the Cathari and Waldenses were condemned. Innocent also ordered a four-year truce among Christian rulers so that a new crusade could be launched.

The fifth Lateran Council, the 18th ecumenical council (1512–17), was convoked by Pope Julius II in response to a council summoned at Pisa by a group of cardinals who were hostile to the Pope. The Pope's council had reform as its chief concern. It restored peace among warring Christian rulers and sanctioned a new concordat with France to supersede the Pragmatic Sanction of Bourges of 1438. In dogmatic decrees the council affirmed the immortality of the soul and repudiated declarations of the councils of Constance and Basel that made church councils superior to the pope (conciliarism). The Orthodox churches do not accept these councils as truly ecumenical.