Pope Callixtus II and Holy Roman Emperor Henry V agree to the Concordat of Worms to put an end to the Investiture Controversy.

Pope Callixtus II or Callistus II, born Guy of Burgundy, was the head of the Catholic Church and ruler of the Papal States from February 1119 to his death in 1124. His pontificate was shaped by the Investiture Controversy, which he was able to settle through the Concordat of Worms in 1122.

Henry V was King of Germany and Holy Roman Emperor, as the fourth and last ruler of the Salian dynasty. He was made co-ruler by his father, Henry IV, in 1098.

The Concordat of Worms, 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.

The Investiture Controversy or Investiture Contest 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.

September 23 is the 266th day of the year in the Gregorian calendar; 99 days remain until the end of the year.