The ancient Greek musical system based on eight “modes” traditionally referred to as the Octoechos also made its way into the practice of the Syriac tradition. In the present article, two experts on Oriental music and liturgy, Jules Jeannin and Julien Puyade, provide an overview of the Octoechos tradition in Syriac. This article was originally published in two parts, but it is combined here into one work. In Part I, Jeannin and Puyade provide a historical survey of the development of the Octoechos from its origins to present practice with particular emphasis on the influence of Bar Hebraeus. In Part II, Jeannin and Puyade discuss the musical features of the Octoechos in Syriac. This discussion includes a comparison with other Oriental musical systems and other forms of Greek music as well. This article serves both as an introduction to the Greek Octoechos tradition and as a comprehensive discussion of its adaptation into the Syriac tradition.