Brasil Island, better known as Hy Brasil, is a phantom island. In the fourteenth century Mediterranean mapmakers marked it on nautical charts to the west of Ireland, and its continued presence on maps over the next six hundred years inspired enterprising seafarers to sail across the Atlantic in search of it. Writers, too, fell for its lure. While English writers envisioned the island as a place of commercial and colonial interest, artists and poets in Ireland fashioned it into a fairyland of Celtic lore. This pioneering study first traces the cartographic history of Brasil Island and examines its impact on English maritime exploration and literature. It investigates the Gaelicization process that the island underwent in nineteenth century and how it became associated with St Brendan. Finally, it pursues the Brasil Island trope in modern literature, the arts and popular culture.