The ways in which saints' cults operated across and beyond political, ethnic and linguistic boundaries in the medieval British Isles and Ireland, from the sixth to the sixteenth centuries, are examined here in a series of case studies. The papers highlight the factors that allowed particular cults to prosper in, or made them relevant to, a variety of cultural contexts. The collection has a particular emphasis on northern Britain, and the role of devotional interests in connecting or shaping a number of polities and cultural identities (Pictish, Scottish, Northumbrian, Irish, Welsh and English) in a world of fluid political and territorial boundaries. Although the majority of the studies are concerned with the significance of cults in the insular context, many of them also touch on the development of pan-European devotions, such as the cults of St Brendan, the Three Kings, or St George.