The Rule of St. Benedict
- Chapters 8-20 are the liturgical code in the Rule of Benedict. On praying the hours.
- http://www.kansasmonks.org/RuleOfStBenedict.html#ch8

Laudis canticum
- Apostolic Constitution, on the promulgation of the revised book of the Liturgy of the Hours, in 1970. By Pope Paul VI.
- http://www.catholicliturgy.com/index.cfm/FuseAction/DocumentContents/Index/2/SubIndex/39/DocumentIndex/372

General Instruction of the Liturgy of the Hours
- Published by the Congregation for Divine Worship in 1971.
- http://www.catholicliturgy.com/index.cfm/FuseAction/DocumentContents/Index/2/SubIndex/39/DocumentIndex/2

John Cassian's Institutes, Book 2
- About evening and night prayer and psalmody.
- http://www.osb.org/lectio/cassian/inst/inst2.html

John Cassian's Institutes, Book 3
- About daytime prayer and psalmody in fourth-century Egyptian monasticism.
- http://www.osb.org/lectio/cassian/inst/inst3.html

Catholic Encyclopedia: Office of the Dead
- Historical article on a special set of prayers for the deceased.
- http://www.newadvent.org/cathen/11220a.htm

An Incentive to Prayer
- Essay by the late Cardinal Spellman says that the publication in English of the official prayer book of the Church offers a tremendous opportunity for anyone who wishes to grow closer to God in prayer.
- http://www.ewtn.com/library/PRAYER/INCENTIV.TXT

"Short" Breviaries in 20th Century America
- Analyzes the breviaria parva, or little hours, based on the Divine Office but adapted for the laity and "active" orders. Presented in order of appearance, compared with the complete Office.
- http://www.kellerbook.com/

Catholic Encyclopedia: Breviary
- Evolution of the book, or set of books, containing the texts and rubrics of the canonical hours.
- http://www.newadvent.org/cathen/02768b.htm

Catholic Encyclopedia: Reform of the Roman Breviary
- Article on the 1911-1913 revamping of the breviary so as to allow recitation of all of the Psalter each week. Feasts were also ranked according to liturgical importance, and some offices were no longer obligatory or were even suppressed.
- http://www.newadvent.org/cathen/16013a.htm

Catholic Encyclopedia: Matins
- Not Morning Prayer, but a nighttime prayer, which has now been replaced by the Office of Readings.
- http://www.newadvent.org/cathen/10050a.htm

Catholic Encyclopedia: Lauds
- Article on the canonical hour once known as Matins, then as Lauds, now as Morning Prayer. One of the two principal hours.
- http://www.newadvent.org/cathen/09038a.htm

Catholic Encyclopedia: Compline
- Scholarly essay on what is essentially a bedtime prayer, often recited privately.
- http://www.newadvent.org/cathen/04187a.htm

Catholic Encyclopedia: Nocturns
- The convoluted history of this nighttime prayer.
- http://www.newadvent.org/cathen/11087b.htm

Catholic Encyclopedia: Music of Vespers
- Applies especially to the cathedral Office, i.e., the Liturgy of the Hours in a parish setting.
- http://www.newadvent.org/cathen/15382a.htm

Catholic Encyclopedia: Vespers
- Historical article on Evening Prayer, one of the two principal canonical hours.
- http://www.newadvent.org/cathen/15381a.htm

Catholic Encyclopedia: None
- Essay on the daytime hour recited in mid-afternoon.
- http://www.newadvent.org/cathen/11097a.htm

Catholic Encyclopedia: Sext
- Article on the midday office.
- http://www.newadvent.org/cathen/13747c.htm

Catholic Encyclopedia: Terce
- Essay on the office of Terce, the earliest of the "little hours" in the day.
- http://www.newadvent.org/cathen/14514c.htm

Catholic Encyclopedia: Prime
- Article on the office of Prime, now suppressed.
- http://www.newadvent.org/cathen/12424a.htm

Catholic Encyclopedia: Divine Office
- Brief essay on the historical development of the Liturgy of the Hours.
- http://www.newadvent.org/cathen/11219a.htm

Catholic Encyclopedia: Canonical Hours
- Essay on the practice of reciting the Divine Office according to set hours.
- http://www.newadvent.org/cathen/07500b.htm

Universalis
- Source for praying the Liturgy of the Hours. Once you have entered your time zone and country, you can bookmark pages for daily prayer. (This site does not use the official Liturgy of the Hours translation due to copyright issues).
- http://www.universalis.com/cgi-bin/display/index.htm

Introduction to the Roman Breviary
- By William J. Lallou. Written in 1950, so the four books he mentions do not correspond to the four-volume set in use today.
- http://www.ewtn.com/library/PRAYER/DIOFFICE.TXT