Our Keltic class of names has presented far greater difficulties. for the Cymric department, I have gathered from many quarters, the safest being Lady Charlotte Guest’s notes to the _Mabinogion_ and M. de Villemarqué’s elucidations of King Arthur’s romances, Rees’s _Welsh Saints_, Williams’s _Ecclesiastical Antiquities_, and Chalmers’s _Caledonia_; the least safe, Davies’s various speculations on British antiquities and the _Cambro-Briton_. These verified by Dr. Owen Pugh’s _Welsh Dictionary_, and an occasional light from Diefenbach and Zeuss, together with a list kindly extracted for me from the _Brut_, have been my authorities in the Welsh and Breton departments. In the Erse and Gaelic names I was assisted by a very kind letter from the lamented Dr. O'Donovan, whose death deprived me of his promised revision of this extremely difficult class, and left me to make it out to the best of my ability from his contributions to the publications of the Archæological Society, from the notes to those of the Ossianic Society, Chalmers’s _Caledonia_, and the Highland Society’s _Gaelic Dictionary_. From the first, however, I had perceived that the curiosity of the study does not lie merely in the meanings of the sounds by which men in one country are distinguished from one another. The changes through which the word passes is one great interest, and for this I had been collecting for years, from dictionaries, books of travels, histories, and popular tales, whenever people were so good as to give the genuine word, instead of translating it into English. Dr. G. Michaelis' _Vergleichendes Wörterbuch der Gebrauchlichsten Taufnamen_ left in me little to desire in this respect, especially with regard to German dialects, and I have used it copiously. The history of names, however, seemed to have been but little examined, nor why one should be popular and another forgotten—why one should flourish throughout Europe, another in one country alone, another around some petty district. Some of these questions were answered by history, some by genealogy, many more by the tracing of patron saints and their relics and legends. Here my great aid has been a French edition of Alban Butler’s _Lives of the Saints_, where, in the notes, are many accounts of the locality and translations of relics; also, Mrs. Jamieson’s _Sacred and Legendary Art_, together with many a chance notice in histories or books of travels. In each case I have tried to find out whence the name came, whether it had a patron, and whether the patron took it from the myths or heroes of his own country, or from the meaning of the words. I have then tried to classify the names, having found that to treat them merely alphabetically utterly destroyed all their interest and connection. It has been a loose classification, first by language, then by meaning or spirit, but always with the endeavour to make them appear in their connection, and to bring out their interest.