This chapter discusses the gradual expansion of the Christian movement into Ireland. Despite widespread fears, the fall of the Roman empire did not herald the end of Christianity. Instead, it encouraged its expansion. Christian missionaries in Ireland worked to ensure that an island with an unfamiliar language and culture beyond the edge of the western empire would accept Christianity more than 100 years before the Anglo-Saxons, and centuries before other northern European peoples. For the fall of Rome and the crisis of imperial Christianity were contexts for the emergence in Ireland, and elsewhere, of a new kind of faith. From the early fifth century, and over several hundred years, the Irish converted to Christianity, shaping their new faith, exporting their theological and missionary cultures, and working for the conversion of the Picts, the Northumbrians, and Anglo-Saxons, as their Christian culture expanded throughout Europe, saving souls, if not ‘saving civilization’, at the end of the Roman world.