As an ancient eastern rite, the Assyrian Church of the East liturgy and music have been the guardian of the Assyrian Christian faith, language and culture for more than a millennium. With the Church’s core activities happening in Mesopotamia, its liturgical music provides additional insight into the history of musical developments in the region, tells the story of Assyrians as a people and culture and recounts their perseverance through a series of persecutions and migrations. Accordingly, this project studies the advancement of several modal systems in the region to determine this tradition’s position in the context of the Middle Eastern music theory. Consequently, this work explores modal aspects of this music and different schools of performance using music analysis and ethnographic data collected in Iraq, Iran, the United Kingdom and the United States. This thesis also studies the role the liturgical music of the Assyrian Church of the East plays in the preservation and presentation of Assyrian ethnic identity, especially after the US invasion of Iraq in 2003 and the rise of ISIS in 2014, by further focusing on the martyrs’ hymn as a chant genre and the relationship between the liturgical language and music. Finally, this study investigates the connection between this musical repertoire and Assyrian musicians through two case studies, including a church musician in Iraq and an Assyrian pop singer in Chicago, to further examine the Church community’s perception of their liturgical music as guardian of tradition and signifier of Assyrianness.