The Latin charters issued by Irish kings in the twelfth and thirteenth centuries, although comparatively few in number, constitute an important body of evidence owing to the scarcity of Irish documentary sources by contrast with narrative, annalistic and literary texts. Their value is greatly enhanced by the fact that chronologically they span the traditional historiographical division between pre-Anglo-Norman and post-Anglo-Norman Ireland and in form are comparable with the charters generated by the English crown and Anglo-Norman settlers in Ireland from 1167 onwards. They therefore contribute to a more balanced assessment of Irish society on the eve on Anglo-Norman intervention in Ireland. The context for the introduction of the Latin charter undoubtedly was the ecclesiastical reform movement that dominated western Christendom from about 1050 onwards and which began to have a discernible impact on the Irish church from no later than c.1100. All the extant Irish royal charters were issued in favour of ecclesiastical beneficiaries and were demonstrably a product of collaboration between Irish kings and reformist clergy. Irish kings, however, were not merely passive recipients of this new documentary reform. They proved adept at exploiting it as a vehicle for their self-promotion and expansion of royal authority. German imperial chancery practice, for example, provided the stylistic model for a charter issued by Diarmait Mac Carthaig, king of Desmond c.1173x7. The known involvement of Diarmait's family with the Schottenklöster of Southern Germany affords a ready explanation for what might otherwise appear to be surprising German influence. The Irish royal charters materially advance understanding of aspects of the ecclesiastical and secular politics of twelfth-century Ireland. This is the first modern edition of the texts, exploring textual transmission and authenticating criteria and providing commentary on their content and historical significance together with detailed annotations of personal and place-names.