Corpus Christi (Latin for Body of Christ) is a Christian feast. Its purpose is to honour the Eucharist, and as such it does not commemorate a particular event in Jesus' life. Its celebration on the Thursday following Trinity Sunday is meant to associate it with Jesus' institution of the Eucharist during the Last Supper, on Maundy Thursday. Because of the sorrow of Holy Week, no festivals are celebrated within it; the Thursday after Trinity Sunday is the first Thursday after Holy Week, Eastertide, and the (now obsolete in the ordinary form) Octave of Pentecost have ended. Within the Roman Catholic Church, the feast is officially known as the Solemnity of the Body and Blood of Christ. In most English-speaking countries, Corpus Christi is transferred to the Sunday after Trinity Sunday by the national Episcopal Conferences. At the end of the Mass, it is customary to have a Procession of the Blessed Sacrament (often outdoors) followed by Benediction of the Blessed Sacrament.
The appearance of Corpus Christi as a feast in the Christian calendar was primarily due to the petitions of the thirteenth-century Augustinian nun Juliana of Liège. From her youth she claimed that God had been instructing her to establish a feast day for the Eucharist and later in life petitioned the learned Dominican Hugh of St-Cher, Jacques Pantaléon (Archdeacon of Liège and later Pope Urban IV) and Robert de Thorete, Bishop of Liège. At that time bishops could order feasts in their dioceses, so in 1246 Bishop Robert convened a synod and ordered a celebration of Corpus Christi to be held each year thereafter. The decree is preserved in Anton Joseph Binterim's Vorzüglichsten Denkwürdigkeiten der Christkatholischen Kirche, together with parts of the first liturgy written for the occasion.
The celebration of Corpus Christi only became widespread after both Juliana and Bishop Robert de Thorete had died. In 1263 Pope Urban IV investigated claims of a Eucharistic miracle at Bolsena, in which a consecrated host began to bleed. In 1264 he issued the papal bull Transiturus in which Corpus Christi was made a feast throughout the entire Latin Rite.
While the institution of the Eucharist is celebrated on Holy Thursday, the liturgy on that day also commemorates Christ's New Commandment ("A new commandment I give unto you, That ye love one another; as I have loved you." ), the washing of the disciples' feet, the institution of the priesthood and the agony in the Garden of Gethsemane. For this reason, the Feast of Corpus Christi was established to create a feast focused solely on the Holy Eucharist.
A new liturgy for the feast was composed by St. Thomas Aquinas. This liturgy has come to be used not only on the Feast of Corpus Christi itself but also throughout the liturgical year at events related to the Blessed Sacrament. The hymn Aquinas composed for Vespers of Corpus Christi, Pange Lingua, is also used on Holy Thursday during the procession of the Blessed Sacrament to the altar of repose. The last two verses of Pange Lingua are also used as a separate hymn, Tantum Ergo, which is sung at Benediction of the Blessed Sacrament. O Salutaris Hostia, another hymn sung at Benediction of the Blessed Sacrament, comprises the last two verses of Verbum Supernum Prodiens, Aquinas' hymn for Lauds of Corpus Christi. Aquinas also composed the propers for the Mass of Corpus Christi, including the sequence Lauda Sion Salvatorem. The epistle reading for the Mass was taken from Paul's First Epistle to the Corinthians and the Gospel reading was taken from the Gospel of John ().
Prior to the liturigcal reforms following the Second Vatican Council, separate feasts existed for the Body of Christ, held on the Thursday after Trinity Sunday, and the Most Precious Blood of Our Lord Jesus Christ, with a feast held on July 1. For those groups currently using the Extraordinary Form of the Roman Rite, the two distinct feasts remain according to the liturgical calendar of the Extraordinary Rite. Until 1955, the Feast of Corpus Christi was followed by a privileged octave.
In medieval times in many parts of Europe Corpus Christi was a popular time for the performance of mystery plays.
The Thursday dates until 2022 are:
Corpus Christi is a public holiday in some traditionally Catholic countries including amongst others Austria, Brazil, Bolivia, Colombia, Croatia, Dominican Republic, East Timor, parts of Germany, Poland, Portugal, San Marino, parts of Switzerland, and Trinidad and Tobago.