The Horologion, also called the Book of Hours, contains the fixed text of those services that follow a fixed daily cycle. Within this framework, moveable parts of the services will be inserted from Holy Scripture, from the Books of Hymns, and from the Synaxarion. Although the services of the Horologion are appointed for specific times throughout the day and night, in practice they are often grouped together. Large monasteries serve all of the services of the Horologion every day; in parishes, only Vespers and Matins are often served regularly, and often only on Sundays, Great Feasts, or other days when the parish will serve Divine Liturgy. The Horologion consists of:
In monasteries that serve the full daily cycle, these services are typically not interspersed throughout the day at their appointed times, but are rather grouped together into morning and evening aggregates. Ninth Hour and Vespers are served together before dinner; Compline is served immediately following dinner; and starting shortly before sunrise the Midnight Office, Matins, First Hour, Third Hour, and Sixth Hour are served. If Divine Liturgy will be served, it follows the Sixth Hour.