This volume focuses on new research on the archaeology of the early medieval Celtic churches c AD 400-1100 in Wales, Ireland, Scotland, south-west Britain and Brittany. The 21 papers use a variety of approaches to explore and analyse the archaeological evidence for the origins and development of the Church in these areas. The results of a recent multi-disciplinary research project to identify the archaeology of the early medieval church in different regions of Wales are considered alongside other new research and the discoveries made in excavations in both Wales and beyond. The papers reveal not only aspects of the archaeology of ecclesiastical landscapes with their monasteries, churches and cemeteries, but also special graves, relics, craftworking and the economy enabling both comparisons and contrasts. They likewise engage with ongoing debates concerning interpretation: historiography and the concept of the Celtic Church, conversion to Christianity, Christianization of the landscape and the changing functions and inter-relationships of sites, the development of saints cults, sacred space and pilgrimage landscapes and the origins of the monastic town.