Liturgia Horarum

The Liturgy of the Hours (Latin: Liturgia Horarum) or Divine Office (Latin: Officium Divinum) or Work of God (Latin: Opus Dei) or canonical hours, often referred to as the Breviary, 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 Eastern and Western traditions (including the Roman Catholic, Eastern Orthodox, Oriental Orthodox, Assyrian, Anglican, Lutheran, and some other Protestant churches) celebrate the Liturgy of the Hours under various names. Within Roman Catholicism, the Liturgy of the Hours, once contained within what was called the Roman Breviary, is in its present form found in what in English editions is called either The Liturgy of the Hours (arranged in four volumes) or The Divine Office (in three volumes).

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