The Liturgy of the Hours (Latin: Liturgia Horarum) or Divine Office (Latin: Officium Divinum) or Work of God (Latin: Opus Dei) or canonical hours,[a] often referred to as the Breviary,[b] is the official set of prayers "marking the hours of each day and sanctifying the day with prayer". It consists primarily of psalms supplemented by hymns, readings and other prayers and antiphons. Together with the Mass, it constitutes the official public prayer life of the Church. The Liturgy of the Hours also forms the basis of prayer within Christian monasticism.
Celebration of the Liturgy of the Hours is an obligation undertaken by priests and deacons intending to become priests, while deacons intending to remain deacons are obliged to recite only a part. The constitutions of religious institutes generally oblige their members to celebrate at least parts and in some cases to do so jointly ("in choir"). The laity are under no public obligation to do so, but may oblige themselves to do so by personal vow, and "are encouraged to recite the divine office, either with the priests, or among themselves, or even individually".
The Liturgy of the Hours, along with the Eucharist, has formed part of the Church's public worship from the earliest times. Christians of both Western and Eastern traditions (including the Latin Catholic, Eastern Catholic, Eastern Orthodox, Oriental Orthodox, Assyrian, Anglican, Lutheran, and some other Protestant churches) celebrate the Liturgy of the Hours in various forms and under various names.
Within the Latin Church, the present official form of the entire Liturgy of the Hours is that contained in the four-volume publication Liturgia Horarum, the first edition of which appeared in 1971. English translations were soon produced and were made official for their territories by the competent episcopal conferences. The three-volume Divine Office, which uses a range of different English Bibles for the readings from Scripture, was published in 1974; the four-volume Liturgy of the Hours, with Scripture readings from the New American Bible, appeared in 1975. Before 1971, the official form for the Latin Church was the Breviarium Romanum, first published in 1568.
In the Byzantine Rite, the corresponding services are found in the Horologion (Ὡρολόγιον), meaning Book of Hours. Anglican Liturgy of the Hours is contained in the book of Daily Prayer of Common Worship and the Book of Common Prayer, as well as in the Anglican Breviary. The Lutheran counterpart is contained in the liturgical books used by the various Lutheran church bodies.