All Orthodox liturgical books can be divided into liturgical (Gospel and Apostle) and church liturgical. The most commonly used book from the second group is Octoech.
It is impossible to imagine the modern Orthodox worship of the daily cycle without the use of the Oktoikh - a book in which the prayers of the main weekly and daily services of eight tones (tunes) are published. Thanks to this content, Octoechus is otherwise called Osmoglassnik.
The octoichus is published in two parts: the first volume contains liturgical texts from the sequences of Vespers, Supper, Midnight Office, Matins and Liturgy from the first to the fourth tones inclusive; the second volume implies the presence of the same divine services of voices from the fifth to the eighth.
Octoichus is used in worship every day for most of the year. Exceptions are periods of great holidays, for example, Easter celebrations. The greatest application of this book relates to the services of Vespers and Matins, which are celebrated in all Orthodox churches. It is in the Octoicha that the stichera, sedals and canons are located, sung or read during the service.
Liturgists date the composition of the Octoichus to the 7th century. It is known that later this book was edited and supplemented by the great saints of the Christian Church. It is worth especially mentioning the Monk John of Damascus, who made the greatest contribution to the formation of Octoichus as an indispensable book for divine services (VIII century).
In each part of the Octoichus there are appendices in which important prayers of individual divine services are published. For example, weekly lamps (on days of the week), 12 gospel stichera of Sunday Matins, as well as the same number of Sunday Exapostilaria and theotokos.
At the present time, in addition to the two volumes, the musical Octoichus can be found. It contains the main chants of the eight voices used in church life.
