“From ancient times the Church has had the custom of celebrating each day the liturgy of the hours. In this way the Church fulfills the Lord’s precept to pray without ceasing, at once offering its praise to God the Father and interceding for the salvation of the world.” — Office of the Sacred Congregation for Divine Worship.
It is prayed in full each day by all men in Holy Orders: bishops, priests and deacons. Consecrated religious who are not priests pray the Office according to the rule of their order. The lay faithful are free to pray it if they wish.
The Divine Office, also known as the Liturgy of the Hours, is the group of psalms, hymns, prayers, biblical and spiritual readings formulated by the Church for chant or recitation at stated times every day. Its origins go back to apostolic times, when it consisted almost entirely of Scripture readings and psalms. Every Catholic priest is required to pray the full daily office. Consecrated Religious who are not priests are obligated according to their rule of life.
Lay faithful are most cordially invited to pray the Divine Office. The Church does not make it obligatory for us, as it is for priests, but if we fully understood what it has to offer, we would make it obligatory upon ourselves.