During May 1910 the substance of this essay in its pan-Celtic form was submitted to the Board of the Faculty of Natural Science of Oxford University for the Research Degree of Bachelor of Science, which was duly granted. But the present work contains considerable material not contained in the essay presented to the Oxford examiners, the Right Hon. Sir John Rhŷs and Mr. Andrew Lang; and, therefore, I alone assume entire responsibility for all its possible shortcomings, and in particular for some of its more speculative theories, which to some minds may appear to be in conflict with orthodox views, whether of the theologian or of the man of science. These theories, however venturesome they may appear, are put forth in almost every case with the full approval of some reliable, scholarly Celt; and as such they are chiefly intended to make the exposition of the belief in fairies as completely and as truly Celtic as possible, without much regard for non-Celtic opinion, whether this be in harmony with Celtic opinion or not. As the new manuscript of the 'Fairy-Faith' lies before me revised and finished, I realize even more fully than I did two years ago with respect to the original study, how little right I have to call it mine. Those to whom the credit for it really belongs are my many kind friends and helpers in Ireland, Scotland, Isle of Man, Wales, Cornwall, and Brittany, and many others who are not Celts, in the three great nations--happily so intimately united now by unbreakable bonds of goodwill and international brotherhood--Britain, France, and the United States of America; for without the aid of all these Celtic and non-Celtic friends the work could never have been accomplished. They have given me their best and rarest thoughts as so many golden threads; I have only furnished the mental loom, and woven these golden threads together in my own way according to what I take to be the psychological pattern of the Fairy-Faith. I am under a special obligation to the following six distinguished Celtic scholars who have contributed, for my second chapter, the six introductions to the fairy-lore collected by me in their respective countries:--Dr. Douglas Hyde (Ireland); Dr. Alexander Carmichael (Scotland); Miss Sophia Morrison (Isle of Man); the Right Hon. Sir John Rhŷs (Wales); Mr. Henry Jenner (Cornwall); Professor Anatole Le Braz (Brittany).