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

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 Salian dynasty or Salic dynasty (German: Salier) was a dynasty in the High Middle Ages. The dynasty provided four kings of Germany (1024–1125), all of whom went on to be crowned Holy Roman emperors (1027–1125).

After the death of the last Ottonian emperor in 1024, the Kingdom of Germany and later the entire Holy Roman Empire passed to Conrad II, a Salian. He was followed by three more Salian rulers: Henry III, Henry IV, and Henry V. They established their monarchy as a major European power. The Salian dynasty developed a permanent administrative system based on a class of public officials answerable to the crown.

Otto II (died 8 November 1111) was a Graf (Count) of Habsburg and one of the founding members of the Habsburg family. He was the son of Werner I, Count of Habsburg. Otto II was likely born in the late 1050s or early 1060s. Otto inherited the county of Klettgau & Altembourg from his father; Werner I, Count of Habsburg.

In 1108, Otto accompanied King Henry V on a campaign against Hungary. On his return, in 1111, he was murdered. Otto is presumed to be the first person to adopt the title Graf von Habsburg.

An Italienzug (also known as Romfahrt or Romzug in German, or as expeditio italica in Latin) was the expedition undertaken by an elected king of the Romans to be crowned by the pope as Holy Roman Emperor in the city of Rome. Prior to the reforms of Frederick Barbarossa, the kings of the Romans struggled to muster an army for the expedition, for they needed the formal approval of the Reichstag. If such approval was granted, the king had permission to recruit knights for their military service in Italy for 410 days.

However, the nobility was generally disinterested and inclined to rather substitute a monetary payment for the service. Therefore, the small force tended to be composed of mercenaries and high ranking clergymen, reinforced by loyal Italian cities. Occasionally, the substitution was not enough – Henry V ended up using his wife Matilda's dowry to fund his Italienzug.

Adalbert I von Saarbrücken (died June 23, 1137) was Archbishop-Elector of Mainz from 1111 until his death. He played a key role in opposing Henry V, Holy Roman Emperor, during the Investiture Controversy, and secured the election of Lothair III rather than Henry V's chosen heir in 1125, causing later Holy Roman Emperors to make concessions in order to maintain hereditary monarchy.