Byzantine chant may be defined as the music used for the celebration of the Byzantine rite, which also has historical links to musical traditions of the Byzantine Empire. This chapter concentrates on the transmission of Byzantine chant, exploring how it was shaped by three factors: oral (performance practices), written (musical notation), and aural (architectural setting). The author argues that the written notation was just a technological vehicle for transmission and not the leading factor in determining the contours of Byzantine chant. By the late twelfth and thirteenth centuries a diastematic system developed, today identified as "the Middle Byzantine notation". It was used to record the melodies of some of the elaborate settings for the cathedral rite of Hagia Sophia. The chapter points to the importance of studying the mechanics of oral–aural chant transmission and the variety of roles played by the written sources in the totality of "chant administration" in its sociological, ritual, and physical contexts.