The Investiture Controversy or Investiture Contest was the most significant conflict between Church and state in medieval Europe. In the 11th and 12th centuries, a series of popes challenged the authority of European monarchies. The issue was whether the pope or the monarch would name (invest) powerful local church officials such as bishops of cities and abbots of monasteries. The conflict ended in 1122, when Emperor Henry V and Pope Calixtus II agreed on the Concordat of Worms. It differentiated between the royal and spiritual powers and gave the emperors a limited role in selecting bishops. The outcome seemed mostly a victory for the pope and his claim that he was God's chief representative in the world. However, the Emperor did retain considerable power over the Church.

The investiture controversy began as a power struggle between Pope Gregory VII (1072–85) and Henry IV, Holy Roman Emperor (1056–1106). A brief but significant struggle over investiture also occurred between Henry I of England and Pope Paschal II in the years 1103 to 1107, and the issue played a minor role in the struggles between church and state in France, as well.