Towards the end of a bardic poem on St Katherine of Alexandria we are presented with a curious list of Gaelic saints, including a stanza on St Brigit, in which she is described as ‘Brighid Éireann agus Alban, ógh na n-oiléan’ (‘Brigit of Ireland and Scotland, Virgin of the Isles’). The bardic poem is anonymous but the sources for the poem rather fittingly include both a Gaelic manuscript from Ireland and a Gaelic manuscript from Scotland. These manuscripts are both dated to the early sixteenth century and are Leabhar Chlainne Suibhne (Dublin, Royal Irish Academy MS 24 P 25) and the Book of the Dean of Lismore (Edinburgh, NLS MS Adv. 72.1.37). The way in which St Brigit is here described is suggestive of a later medieval pan-Gaelic piety, common to both Ireland and Gaelic Scotland. This chapter will consider if the rest of the religious poetry from the Scottish Book of the Dean of Lismore is as representative of such a pan-Gaelic piety. We will explore the context of Gaelic manuscript compilation before concentrating on the Book of the Dean’s collection of religious poetry. The main aim is to detail the poems which are found therein and investigate which poems are unique to Scotland and which are common to Scotland and Ireland. Further, since Gaelic manuscripts often show antiquarian tendencies we will also focus on when the Book of the Dean religious poetry was composed and how this impacts on our notions of later medieval piety. This chapter will conclude by introducing some of the major themes of its religious poetry.