The Fairy-Faith in Celtic Countries is a study by W. Y. Evans-Wentz, American anthropologist who studied Celtic mythology and folklore. He performed ethnographic fieldwork collecting fairy folklore in Wales, Scotland, Ireland, Cornwall, Brittany, and the Isle of Man, and in this book he published his degree thesis. His goal was to elucidate the phenomenon of the Celtic belief in fairies. Some of the theories he came across are that the fairies were a cloistered race of dwarfs, that they are a product of our imagination, or that they are incorporeal spirits.