octoechos

Octoechos, also written Oktoechos, is the system of eight mode families used in Byzantine liturgical chant and in many Orthodox Christian musical traditions. The name derives from Greek oktōechos, “eight sounds.” The eight echoi are divided into four authentic modes (protos, deuteros, tritos, tetartos) and four plagal modes (plagios protos, plagios deuteros, plagios tritos, plagios tetartos). Each echos has a characteristic final pitch and typical melodic range, and a set of melodic formulas that guide melodic movements and cadences. The same melody can be adapted to different texts within a mode, giving a coherent sound to hymns such as stichera, canons, and kontakia.

In the liturgical year, the octoechos provides a rotating framework: the daily and festive hymns are assigned to one of the eight tones, creating a recurring weekly cycle that varies the melodic character of services. The Octoechos is also the name of a liturgical book that organized the chant material by mode, used across the Byzantine Rite and in related Orthodox rites, including the Church Slavonic and Greek practices.

Historically, the octoechos system developed in the Byzantine world during the first millennium and was expanded and codified in the Middle Ages. It influenced later theories of modality in Orthodox and some Western medieval traditions and remains central to the melodic organization of Byzantine chant today.