The Investiture Controversy, also known as the lay investiture controversy, was the most important conflict between secular and religious powers in medieval Europe. It began as a dispute in the 11th century between the Holy Roman Emperor Henry IV (1050-1106) and the Gregorian papacy of Pope Gregory VII (1073-1085) over who would control appointments of church officials. By undercutting the claims of imperial power, the controversy led to nearly 50 years of bitter Civil War and the disintegration of Germany, as many German Lords used this time to increase their own power and embark on a castle building programme which in turn weakened the power of the Holy Roman Emperor, something from which he never really recovered, marking the end of the Early Middle Ages with the "final and decisive" acceptance of Christianity by the Germanic peoples, setting the stage for the religious and political system of the High Middle Ages.
There was also a brief but significant investiture struggle in the 12th century between Pope Paschal II (1099-1118) and King Henry I of England (1100-1135) from 1103 to 1107.
The investiture conflict ended in 1122, when Pope Callixtus II (c. 1065 – 13 December 1124) and Emperor Henry V (1111–25) agreed on the Concordat of Worms (September 23, 1122), which differentiated between the royal and spiritual powers and gave the emperors a limited role in selecting bishops. The outcome was largely a papal victory, but the Emperor still retained considerable power.
- Henry IV, Holy Roman Emperor in Europe, not to be confused with Henry IV of England.