Building from the premise that hagiographical texts provide important literary accounts of affective religious experiences in the medieval centuries, this dissertation examines the nine homiletic saints’ lives in the fifteenth-century Book of Lismore. Specifically, the focus is on representations of the Eucharist, the axiomatic sacrament of Latin Christendom in the eleventh and twelfth centuries, and how writers of and audiences for these Middle Irish texts perceived, or were intended to apprehend, the role of Communion in constructing and affirming their Christian identities. Throughout this work attention is drawn to parallels with and divergences from European Eucharistic orthodoxy and orthopraxy in the period contemporary with the texts’ composition. This dissertation is divided into six chapters: the first two offer important historical, literary and theological context for the texts which are the foundation of this enquiry, together with new insights into the scholarly profit to be derived from including vernacular hagiography in the corpus of texts mobilised in the study of theological developments of this period; the next three chapters examine specific dimensions of Christian identity - clerical, gender and lay; the sixth and concluding chapter synthesises the analysis of the foregoing sections. Chapter I outlines the significance of the Eucharist in medieval religious life and its relationship to the reform impetuses of the long twelfth-century. The categorisation of the nine Lismore Lives as homilies is not uncontested and this work offers a comprehensive defence of that classification by reference to the extant corpus of Irish homiletic literature and internal structural and stylistic features of the core texts. A section of the chapter addresses questions of dating and advances arguments that situate seven of the nine texts broadly within the period 1050–1200, by amalgamating and augmenting existing research undertaken on individual saints’ Lives. In Chapter II, the focus is on both the literary and linguistic content of a number of contemporary homiletic and theological tracts and how these relate both to contemporaneous European debates on the Real Presence and the long tradition of Irish exegesis and religious speculation. Particular attention is paid to texts, and episodes within texts, from a diverse range of genres, that have not previously been adduced in discussions of Irish Eucharistic doxa and praxis. The final portion of II provides an overview of the origins and development of a select portion of the vernacular vocabulary of the Eucharist and the theological implications of those semantic choices. Chapters III–V investigate three of the most significant medieval identity markers, as they intersect with corporate Christian identities. Chapter III provides a thorough-going overview of the clerical identities constructed for the male Lismore saints and attempts to differentiate the role of the Eucharist in the emergent episcopal identities of this period. Attention is also given to the significant role of viaticum in the texts and the inferences, on Irish perceptions of Eucharistic efficacy, we may draw from this. The primary focus of the fourth chapter is gendered Eucharistic narratives and important episodes from Betha Shenáin are analysed. Evidence is presented to suggest that gender demarcated not only the authority to perform the Eucharistic rite but also access to Communion. In Chapter V, Betha Bhrénainn is mined for details of lay and penitent Communication. The substantial intertextual relationships which exist between Brendan’s Betha and voyage literature provide the foundation from which to consider how medieval and modern readings of content potentially were, and remain, inflected by genre classifications. Chapter VI is a synthesis of the conclusions arising from the forgoing chapters and offers a tentative thesis on the extent to which these hagiographical depictions can be argued to provide a synoptic view of concomitant Eucharistic and reform ideologies, concluding ultimately that the results are pluriform rather than uniform. Finally, attention is drawn to how future research questions on Irish Eucharistic thought and practices might be better designed, given the insights which have arisen from this project.