Pope Callixtus II in the context of "Henry V, Holy Roman Emperor"

The Investiture Controversy or Investiture Contest (Latin: Controversia de Investitura, German: Investiturstreit, pronounced [ɪnvɛstiˈtuːɐ̯ˌʃtʁaɪt] ) was a conflict between the Church and the state in medieval Europe over the ability to choose and install bishops (investiture), abbots of monasteries, and the Pope himself. A series of popes in the 11th and 12th centuries undercut the power of the Holy Roman Emperor and other European monarchies, and the controversy led to nearly 50 years of conflict.

It began as a power struggle between Pope Gregory VII and Henry IV (then King, later Holy Roman Emperor) in 1076. The conflict ended in 1122, when Pope Callixtus II and Emperor Henry V agreed on the Concordat of Worms. The agreement required bishops to swear an oath of fealty to the secular monarch, who held authority "by the lance" but left selection to the church. It affirmed the right of the church to invest bishops with sacred authority, symbolized by a ring and staff. In Germany (but not Italy and Burgundy), the Emperor also retained the right to preside over elections of abbots and bishops by church authorities, and to arbitrate disputes. Holy Roman Emperors renounced the right to choose the Pope.

The Concordat of Worms (Latin: Concordatum Wormatiense; German: Wormser Konkordat), also referred to as the Pactum Callixtinum or Pactum Calixtinum, was an agreement between the Catholic Church and the Holy Roman Empire which regulated the procedure for the appointment of bishops and abbots in the Empire. Signed on 23 September 1122 in the German city of Worms by Pope Callixtus II and Emperor Henry V, the agreement set an end to the Investiture Controversy, a conflict between state and church over the right to appoint religious office holders that had begun in the middle of the 11th century.

By signing the concordat, Henry renounced his right to invest bishops and abbots with ring and crosier, and opened ecclesiastical appointments in his realm to canonical elections. Callixtus, in turn, agreed to the presence of the emperor or his officials at the elections and granted the emperor the right to intervene in the case of disputed outcomes. The emperor was also allowed to perform a separate ceremony in which he would invest bishops and abbots with a sceptre, representing the lands that constituted the temporalities associated with their episcopal see.

William I (1020 – 12 November 1087), called the Great (le Grand or Tête Hardie, "the Stubborn"), was Count of Burgundy from 1057 to 1087 and Mâcon from 1078 to 1087. He was a son of Reginald I, Count of Burgundy and Alice of Normandy, daughter of Richard II, Duke of Normandy. William was the father of several notable children including Pope Callixtus II.

In 1057, William succeeded his father and reigned over a territory larger than that of the Franche-Comté itself. In 1087, he died in Besançon, Prince-Archbishopric of Besançon, Holy Roman Empire—an independent city within the County of Burgundy. He was buried in Besançon's Cathedral of St John.

The First Council of the Lateran was the 9th ecumenical council recognised by the Catholic Church. The first ecumenical council to be held in Western Europe and the first since the Great Schism of 1054, it was convoked by Pope Callixtus II in December 1122, immediately after the Concordat of Worms. The council sought to bring an end to the practice of the conferring of ecclesiastical benefices by people who were laymen, free the election of bishops and abbots from secular influence, clarify the separation of spiritual and temporal affairs, re-establish the principle that spiritual authority resides solely in the Church and abolish the claim of the Holy Roman Emperor to influence papal elections.

The council was significant in size: 300 bishops and more than 600 abbots assembled at Rome's Lateran Palace in March 1123, and Callixtus II presided in person. During the council, the decisions of the Concordat of Worms were read and ratified. Various other decisions were promulgated.