This dissertation concerns the narrative and theological role of divine vengeance and saintly cursing in the saints’ Lives of England and Ireland, c. 1060-1215. The dissertation considers four case studies of primary material: the hagiographical and historical writings of the English Benedictines (Goscelin of Saint-Bertin, Eadmer of Canterbury, and William of Malmesbury), the English Cistercians (Aelred and Walter Daniel of Rievaulx, John of Forde), the cross-cultural hagiographer Jocelin of Furness, and the Irish (examining key textual clusters connected with St. Máedóc of Ferns and St. Ruadán of Lorrha, whose authors are anonymous). This material is predominantly in Latin, with the exception of the Irish material, for which some vernacular (Middle Irish) hagiographical and historical/saga material is also considered. The first four chapters (I-IV) focus discretely on these respective source-based case studies. Each is framed by a discussion of those textual clusters in terms of their given authors, provenances, audiences, patrons, agendas and outlooks, to show how the representation of cursing and vengeance operated according to the logic of the texts and their authors. The methods in each case include discerning and explaining the editorial processes at work as a basis for drawing out broader patterns in these clusters with respect to the overall theme. The fifth chapter (V) frames a more thematic and comparative discussion of the foregoing material, dealing with the more general questions of language, sources, and theological convergences compared across the four source bases. This chapter reveals in particular the common influence and creative reuse of key biblical texts, the Dialogues of Gregory the Great, and the Life of Martin of Tours. Similar discussion is made of a range of common ‘paradigms’ according to which hagiographical vengeance episodes were represented. In a normative theology in which punitive miracles, divine vengeance and ritual sanction are chiefly understood as redemptive, episodes in which vengeance episodes are fatal can be considered in terms of specific sociological imperatives placing such theology under pressure. The dissertation additionally considers the question of ‘coercive fasting’ as a subset of cursing which has been hitherto studied chiefly in terms of the Irish material, but which can also be found among the Anglo-Latin writers also. Here it is argued that both bodies of material partake in an essentially shared Christian literary and theological culture, albeit one that comes under pressure from particular local, political and sociological circumstances. Looking at material on both sides of the Irish Sea in an age of reform, the dissertation ultimately considers the commonalities and differences across diverse cultural and regional outlooks with regard to their respective understandings of vengeance and cursing.