This publication is the first interdisciplinary collection of articles focusing on religion and mythology in Celtic studies. The first part presents various current viewpoints within the field from scholars of history, art history and literary studies. In addition to more traditional approaches, the other two parts of the book illustrate the possibilities of applying new theories and methods from the discipline of Comparative Religion to the analysis of Celtic materials. They introduce previously unpublished results of the international research network “The Power of Words in Traditional European Cultures”, and the research project “Religion, Society, and Culture: Defining the Sacred in Early Irish Literature” funded by the Academy of Finland at University of Helsinki. The present collection serves as a significant contribution towards a better understanding of issues that have not been previously brought together in a single volume. As such it is of interest to scholars in Celtic studies as well as other related disciplines.