This study provides a fascinating look at the various ways in which 20th-century fantasy writers have used Welsh Celtic mythology and folklore in their work. Following the theories formulated by such scholars as John Vickery and Joseph Campbell, the use of Celtic materials by each of the authors is discussed from a mythology-in-literature perspective. Sullivan presents an extensive accounting of the Celtic material used and explores the primary ways in which the authors incorporate it into their fiction, both structurally and thematically. Sullivan identifies and analyzes the nature and extent of Welsh Celtic influence on subsequent cultures and their literatures, and he considers some of the previous attempts to evaluate this influence. The appendixes provide valuable background materials, including critical commentary on the Welsh collection of myths, legends, folktales, and beliefs that are of major importance in the work of the six authors represented. Also included are extensive bibliographies of primary and secondary sources. Illuminating reading for students and scholars of mythology, modern fantasy, and children's literature, this book sheds new light on the Welsh influence in literature and opens paths for further research.