The First Crusade inspired the crusading movement, which became an important part of late-medieval western culture. The movement influenced the Church, politics, the economy, society, and created a distinct ideology that described, regulated, and promoted crusading. It was defined by legal and theological terms based on the concepts of holy war and pilgrimage. Theologically, the movement merged ideas of Old Testament wars instigated and assisted by God with New Testament ideas of forming personal relationships with Christ. The concept of crusading as holy war was based on the ancient idea of just war, in which an authority initiates the war, there is just cause, and the war is waged with pureness of intention. Crusades were seen as special pilgrimages—a physical and spiritual journey under the authority and protection of the Church. Pilgrimage and crusade were penitent acts and Crusade participants were considered part of Christ's army. While this was only metaphorical before the First Crusade, the concept was transferred from the clergy to the wider world. Crusaders attached crosses of cloth to their outfits, marking them as followers and devotees of Christ, responding to the biblical passage in Luke 9:23 which instructed them to carry one's cross and follow Christ. Anyone could be involved and those who died campaigning were considered martyrs.

Crusading was strongly associated with the recovery of Jerusalem and the Palestinian holy places. The Holy Land was considered the patrimony of Christ, and its recovery was on the behalf of God. The historic Christian focus on Jerusalem as the setting for Christ's act of redemption was fundamental for the First Crusade and the successful establishment of the institution of crusading. Campaigns to the Holy Land had enthusiastic support. The Crusading movement expanded to other theatres on the periphery of Christian Europe: the Iberian Peninsula; north-eastern Europe, against the Wends; the Baltic region; against heretics in France, Germany, and Hungary; and into mainly Italian campaigns against the papacy's political enemies. Common to all was papal sanction and the medieval concept of one Christian Church ruled by the papacy and separate from non-believers, so that Christendom was geopolitical.

Crusading was a paradigm that grew from the encouragement of the Gregorian Reform of the 11th century and the movement declined after the Reformation. The ideology continued after the 16th century but in practical terms dwindled in competition with other forms of religious war and new ideologies.