melody type associated with early Byzantine liturgical chant. The eight ēchoi (hence, the collective oktōēchos) of the Byzantine system were probably derived from Syrian (Syrian chant) music, and the concept of ēchos is also found in Armenian, Russian, and Coptic chant. Tradition gives credit to St. John of Damascus (d. 749) for the invention of the eight Byzantine ēchoi, but the oktōēchos is mentioned already in an early 6th-century Syrian source.

The ēchoi are not scales but groups of melodic formulas that can be combined to form entire melodies. In a collection of Greek kanōnes (hymns), each melody is classified according to the ēchos from which formulas were selected for its composition. Like the eight modes of Gregorian chant, the ēchoi are grouped in four pairs. Oktōēchos is also used to refer to a collection of liturgical songs, arranged according to the ēchos to which each text is set.