Conversion to Christianity is arguably the most revolutionary social and cultural change that Europe experienced throughout Late Antiquity and the early Middle Ages. Christianisation affected all strata of society and transformed not only religious beliefs and practices, but also the nature of government, the priorities of the economy, the character of kinship, and gender relations. It is against this backdrop that an international array of leading medievalists gathered under the auspices of the Converting the Isles Research Network (funded by the Leverhulme Trust) to investigate social, economic, and cultural aspects of conversion in the early medieval Insular world, covering different parts of Britain, Ireland, Scandinavia, and Iceland. This is the first of two volumes showcasing research generated through the Network's activities. This volume focuses on specific aspects of the introduction of Christianity into the early medieval Insular world, including the nature and degree of missionary activity involved, socio-economic stimulants for conversion, as well as the depiction and presentation of a Christian saint. Its companion volume has the transformation of landscape as its main theme. By adopting a broad comparative and cross-disciplinary approach that transcends national boundaries, the material presented here and in volume II offers novel perspectives on conversion that challenge existing historiographical narratives and draw on up-to-date archaeological and written evidence in order to shed light on central issues pertaining to the conversion of the Isles.