'''''Octoechos''''' (from Greek '''οκτοηχος''') can refer either to the eight-[[tone]] (or mode) system of Church music or to the [[liturgical books|liturgical book]] containing the weekly variable texts in each of the eight tones. St. [[John of Damascus]] is credited with the systemization of the musical forms of the Church.
In Greek usage, the ''Octoechos'' book is only the Resurrectional material for [[Sunday]] services which varies in the eight-week cycle, and thus is also called the '''''Anastasimatarion'''''. The Greek book for all seven days of the weekly material is the '''''Parakletiki'''''. In Slavic usage, the ''Octoechos'' (or ''Oktoich'') book includes the material for every day of the week, and thus is equivalent to the Greek ''Parakletiki''.
The final form of the ''Parakletiki'' was significantly influenced by the 9th century St. [[Joseph the Hymnographer]].
* [[Church Music]]
*[http://www.anastasis.org.uk/oktoich.htm Paraklitiki (Arch. Ephrem (Lash))]
*[http://www.st-sergius.org/services/services2.html Sunday Octoechos (Traditional English)]