Breviary means 'what is abridged'. In early monasticism there were separate volumes for the various parts of the Divine Office; the Psalter contained the psalms, the lectionary the readings, and the collectary the orations or prayers (also called collects). From the 11th century, these were abridged and compressed into smaller volumes, each containing all the parts, and the division into volumes following the liturgical seasons. This abridged form of the office came to be known as the Breviarium or Breviary, from the Lain word brevis meaning 'short'.

There has been Breviary reform in the Church from time to time, notably by Pope St. Pius V in 1568, by Pope St. Pius X in 1911 and by Vatican II. In keeping with the latter Council's Constitution on the sacred liturgy, the Breviary was simplified and its use made liturgically more meaningful.

With regard to the obligation on the part of the priest to recite the Breviary Vatican II says: "Priests engaged in the sacred pastoral ministry will offer the praises of the hours with fervour to the extent that they vividly realize that they must heed St. Paul's exhortation: "Pray without ceasing" (1 Th.5:17). For only the Lord can give fruitfulness and increase to the works in which they are engaged. 'Without me' he said, 'you can do nothing'. (Jn 15:5). That is why the apostles, appointing deacons said: "We will devote ourselves to prayer and to the ministry of the world." (Acts 6:4).

The law of the Church lays it down that "priests and deacons aspiring to the priesthood are obliged to carry out the liturgy of the hours daily, in accordance with their own approved liturgical books." (Can. 276:2,3).

Apart from monks and those in Holy Orders, the celebration of the Hours is carried out also by religious men and women professed for choir duties, that is, the performance of the liturgical Hours.

By the recitation of the Breviary, the priest, united with brother priests and choir religious all over the world, raises to God throughout the day a prayer of adoration, thanksgiving, contrition for sin and petition, supplementing as it were the prayers of his daily Mass.