On the occasion of the fifteenth centenary of St Patrick, in 1932, Eoin MacNeill made, not a ‘call to arms’ but a ‘call to scholarship’ in ‘A School of Irish Church History’. As the title suggests, 1 this was an exercise in advocating for the timely establishment of a ‘school’, in the sense of the ‘conscious collaboration’ of scholars, researching the history of the Church in Ireland. His 2 dedication to early Irish history dominated his later life and ‘post-political’ career. Given his explicitly expressed desire that the history of the Church in Ireland be studied on a large scale, as a dedicated effort, one could wonder why MacNeill did not tackle the subject himself as a distinct object of study. Although his work played a pivotal role in forming our modern understanding of many areas of early Irish history, including the Church, he barely mentions this institution in his three popular book-length publications Celtic Ireland, Phases of Irish History and, perhaps most curiously, Early Irish Laws and Institutions. The impression is that he felt it was important to determine certain ‘truths’ first, for 3 example to establish a firm foundation of the history of Ireland before the arrival of Christianity. He stated that a general history of Ireland was something requested of him, but that such an undertaking was ‘still premature’. He referred to J.F. Kenney’s great bibliographic work on the ecclesiastical sources for 4 early Irish history as one of the vital contributions that would make such a work feasible. Kenney’s 5 book, despite its age and limitations, is still a useful starting point for students of early Ireland and it has only recently been superseded by Donnchadh Ó Corráin’s monumental survey of written sources produced by medieval Irish writers, the Clavis Litterarum Hibernensium. At three volumes and over 6 two thousand pages, the Clavis epitomises the challenges and opportunities facing the scholar of early Irish history. MacNeill was, perhaps, one of the first scholars with the skill and desire to take on these sources and demonstrate their worth. This paper will explore MacNeill’s contributions to our understanding of the history of the early Irish Church and how this influenced the development of the field in subsequent decades.