Wales has a significant number of islands that have supported monastic life at some time in their histories. These monastic islands do not command quite the same international attention as those from other Celtic nations, for example Skellig Michael (Ireland) or Iona (Scotland), but islands such as Ynys Enlli (Bardsey) and Caldey Island (Ynys Bŷr) have sustained recognition as 'holy islands' in Welsh tradition. Those seeking assessments of the phenomenon of island monasticism in Wales will also find only a modest literature, now requiring some careful recalibration in the light of changing interpretations of Welsh church history. This discussion is an attempt to establish the data and models for a holistic reassessment. This is not necessarily just an academic desideratum. Welsh islands have recently, for example, been identified as assets for the emerging trend of 'faith tourism', with potential economic as well as environmental impact.<br/> In this study I will approach the archaeology of the Welsh islands initially by way of their historical context. There are a number of reasons for this choice of approach. It is arguable that only a multi-disciplinary approach here offers a sustainable body of data for analysis. Island sites are characteristically materially poor and the eremitical ethos of much island monasticism converges with that tendency. The 'island monastery' is also prone to rather singular conception as an 'early Christian' artefact, whereas much of what we think we know concerning the Welsh islands speaks most definitely of later medieval use—and only uncertainly of the early medieval. So a strongly diachronic approach is essential. For one or two of the islands, moreover, there is a requirement simply to resolve their historical identities. Finally, there is a pressing need to uncouple these islands from dated historical models of evangelism via the seaways and other models in which monasticism is conflated with secular Christianity—assumptions that can influence interpretation of archaeological evidence for settlement.