The practice of Eucharistic adoration is a devout prayer before the body of Christ in the Eucharist, displayed outside of the context of the Mass. Once a very widespread practice, it became less popular after the second Vatican Council, which placed a greater emphasis on the active participation of the faithful in the liturgy itself. In the 21st Century, adoration is growing in popularity once again. But the origins of Eucharistic adoration are not very well known.
One of the first references to reserving the Blessed Sacrament for adoration is in the life of St. Basil the great in the late fourth century. It is said that St. Basil divided the consecrated Eucharistic bread into three parts during the liturgy at his monastery. One part he consumed himself, the second was given to the monks, and the third portion was placed in a Golden Dove suspended above the altar. It seems likely that this reserved portion was kept for those who were unable to attend the liturgy because of illness or travel, for instance.
The practice of Eucharistic adoration among laypeople is thought to have begun in Avignon, France, on September 11 1226. King Louis VII, having just won a victory over the Albigensians, asked that the Blessed Sacrament be placed on display at the Chapel of the Holy Cross. This exposition was so popular that the local bishop asked to have it continue indefinitely. Pope Honorius II gave his assent and the practice continued there nearly uninterrupted until the French Revolution in 1792.
Although some liturgical theologians find Eucharistic adoration somewhat at odds with the purpose and practice of the Eucharist at Mass — that is to say Communion — in recent years Eucharistic adoration has become more popular, particularly among younger Catholics. The longest running Eucharistic adoration in the United States is with the Franciscan sisters of perpetual adoration in La Crosse Wisconsin, who have been praying nonstop for more than 130 years.