Priests and religious are obligated to pray several times a day in the Catholic Church; many lay people also pray the Liturgy of the Hours. From the Wikipedia page I linked above:
Traditional Roman Breviary
By the end of the fifth century, the Liturgy of the Hours was composed of seven offices, of which Compline seems to be the last to appear, since the fourth-century Apostolic Constitutions VIII, iv, 34 do not mention it in the exhortation: "Offer up your prayers in the morning, at the third hour, the sixth, the ninth, the evening, and at cock-crowing".[3]
An eight hour, Prime, was added by Benedict of Nursia in the sixth century. These eight hours are known by the following names:
Saint Benedict of Nursia (c. 480 – 543) is credited with having given this organization to the Liturgy of the Hours. However, his scheme was taken from that described by John Cassian, in his two major spiritual works, the Institutes and the Conferences, in which he described the monastic practices of the Desert Fathers of Egypt. Taylor Marshall has demonstrated how these Christian cycles of daily prayer derived from Jewish customs of prayer.[4]
- Matins (during the night, at midnight with some), sometimes referred to as Vigils or Nocturns, or in monastic usage the Night Office; in the Breviary of Paul VI it has been replaced by the Office of Readings
- Lauds or Dawn Prayer (at Dawn, or 3 a.m.)
- Prime or Early Morning Prayer (First Hour = approximately 6 a.m.)
- Terce or Mid-Morning Prayer (Third Hour = approximately 9 a.m.)
- Sext or Midday Prayer (Sixth Hour = approximately 12 p.m.)
- None or Mid-Afternoon Prayer (Ninth Hour = approximately 3 p.m.)
- Vespers or Evening Prayer ("at the lighting of the lamps", generally at 6 p.m.)
- Compline or Night Prayer (before retiring, generally at 9 p.m.)
[edit] Liturgy of the Hours of Paul VI
Benedictine monks singing Vespers on Holy Saturday
After the Second Vatican Council, Pope Paul VI promulgated a new Roman Breviary, commonly referred to as "Liturgy of the Hours". In this Breviary, the structure of the offices, the distribution of psalms and the prayers themselves were heavily modified. Prime was suppressed entirely and Matins was replaced by the new Office of Readings.
Its usage focuses on three major hours and from two to four minor hours:
- The Officium lectionis or Office of Readings (formerly Matins), major hour
- Lauds or Morning prayer, major hour
- Daytime prayer, which can be one or all of:
- Terce or Mid-Morning Prayer
- Sext or Midday Prayer
- None or Mid-Afternoon Prayer
- Vespers or Evening Prayer, major hour
- Compline or Night Prayer