It presents an investigation into the liturgical music of Sean and Peadar O Riada through an examination of three Roman-Rite mass settings composed in the Irish vernacular from within the cultural context of the West-Cork Gaeltacht of Muscrai. The main part of the work, running from Chapters Three to Six, consists of a detailed analysis of the contents of the mass settings, a body of material which is considered from the following perspectives: as emanating from a living culture of native traditional song; as part of a historical continuum of monophonic liturgical composition for the Roman Rite, having at its origins the compositional traditions of plainchant; as part of a broader aesthetic context of text-music relationships found in the repertoires of plainchant, medieval song and folksong; and finally, as part of the new liturgical reality existing since the Second Vatican Council which requires viable and sustainable musical approaches to the setting of vernacular texts.