The Liturgy of the Hours, Divine Office, or Opus Dei are a set of Catholic prayers comprising the canonical hours, often also referred to as the breviary, of the Latin Church. The Liturgy of the Hours forms the official set of prayers "marking the hours of each day and sanctifying the day with prayer." The term "Liturgy of the Hours" has been retroactively applied to the practices of saying the canonical hours in both the Christian East and West–particularly within the Latin liturgical rites–prior to the Second Vatican Council, and is the official term for the canonical hours promulgated for usage by the Latin Church in 1971. Before 1971, the official form for the Latin Church was the Breviarium Romanum, first published in 1568 with major editions through 1962.

In the practice of Christianity, canonical hours mark the divisions of the day in terms of fixed times of prayer at regular intervals. A book of hours, chiefly a breviary, normally contains a version of, or selection from, such prayers.