This study is concerned with the vocal iso(n) repertory, used, on the one hand, in the oral traditions of the multipart unaccompanied singing (IMUS) of the Southwest Balkans, or, more specifically, South Albania, North Epirus in Greece and a small part of the Republic of Macedonia (FYROM), and on the other hand in Byzantine chanting. The vocal iso(n) is an important component of these traditions, which are still practised today in the Southwest Balkans region. The study presents evidence on various manifestations of the practice in their particular geographical regions, and examines in detail the historical roots of these traditions. An ison, a drone holding-note, is the voice that provides the drone in Byzantine chanting. This chant is part of the liturgical music of the Orthodox Churches, in contrast to the IMUS, which has developed as a secular repertory. The Byzantine liturgical singing of the Arbëresh Diaspora of South Italy and Sicily, which has been passed down orally from the 15th century to the present day, as well as non-liturgical singing, is also explored in this book. The three unaccompanied forms of singing, two of which use the ison (IMUS and Byzantine chanting) and the third, the Arbëresh, which does not (with some exceptions in recent times), are analysed in separate sections of the book