This chapter examines the considerable impact that Irish mythology had upon the work of C.S. Lewis. Biographers and critics are always ready to discuss Lewis’s debts to Greek and Norse mythology, but the sagas and heroic tales from Lewis’s native Ireland are usually glossed over quickly in analysis of his fiction and poetry. This is remarkable when one considers how many of Lewis’s works centrally incorporate figures, objects, and tropes from Irish mythological and legendary literature. For example, multiple characters from the Ulster Cycle, the Fenian Cycle, and the Mythological Cycle are namechecked in Lewis’s first poetry collection Spirits in Bondage (1919) and its earlier incarnation as the manuscript Metrical Meditations of a Cod (which, of course, bears quite an Irish title); many of the plot points and character portraits in The Voyage of the Dawn Treader (1952) are borrowed from the medieval Irish manuscripts detailing the adventures of St. Brendan, the legendary Kerry sailor-monk; and certain aspects of the life and character of the central protagonist in Till We Have Faces (1956) are derived from the life and character of Queen Maeve of Connaught, as outlined in the Ulster Cycle.