These are the books I think of as a basic “starter kit” for Celtic Studies. Many of the “standards,” those books that have been considered essential reading, are now out of print. They are still current and worth having, so I’m still going to recommend them. You’ll notice that created two separate lists, the “starter” kit, and a short list of a few more “advanced” or secondary books.
If you only want a one book that offers a survey or general overview:
Cunliffe, Barry. The Celts: A Very Short Introduction. Oxford University Press: Oxford, 2003. ISBN: 0192804189. ISBN-13: 978-0192804181.
This is exactly what the title suggests; a very short introduction, but it’s a thorough survey of Celtic history and culture, from a leading archaeologist and expert on the ancient Celts. It’s readable, accurate in spite of its brevity, and a good review for those looking for the current research and theories, as well as a solid introduction for those who have interest but neither time nor money for the larger tomes. I wrote a longer review here.
If I had to list the must haves, I personally find the following books essential:
The Celtic Studies Starter Kit
The Mabinogi are the four Welsh mythological tales. Ford doesn’t include the romances, which aren’t part of the Mabinogi proper, but he does include the four branches, the native tales, and Taliessin material that is not available elsewhere in English. I think his introduction alone is worth the price of the book, and his translation is faithful to the tone and text of the Welsh, and easier to enjoy than any other.
Gantz, Jeffrey. Early Irish Myths and Sagas. London:
Penguin Books, 1981. ISBN 0140443975. Gantz offers his own abbreviated translation of the Tain, as well as most of the central Ulster tales and a few of the mythic sagas.
Thomas Kinsella. The Tain. Oxford: Oxford University Press, 1970. ISBN 0192810901. Simply the most readable English translation going of the Irish national epic, and the associated main mythological tales.
Koch, John T. and John Carey eds. The Celtic Heroic Age.
Malden, Massachustetts: Celtic Studies Publications, 2003. Fourth edition. ISBN 1891271091. The sub-title describes the book: “Literary sources for ancient Celtic Europe and Early Ireland and Wales.” The work of two leading Celticists (though Koch is the prime mover), it discusses the Classical and Gaulish materials, as well as the literary materials of Wales and Ireland with a nod at Breton material. The text is thematically organized, and offers a good introduction to the cultural background of Irish and Welsh literature, and is particularly useful for its presentation of Classical texts. You can order the book directly from the publisher, using the link above.
MacKillop, James. Dictionary of Celtic Mythology. Oxford: Oxford University Press, 1998. ISBN 0192801201. There are a lot of “dictionaries” of Celtic myth out there; I’ve decided to recommend this one. No, it’s not perfect, but the only real competition it has is from Miranda Green’s Dictionary. Green’s book, though I do like it for its lovely images, is a bit too idiosyncratic in some of Green’s personal interpretations, which are not always clearly presented as personal interpretations. Ideally, one would want both books, but MacKillop, who includes a bibliography as well as citations, is more likely to be reliable and good for the long term, and it’s far superior to that of Ellis, who is somewhat careless, frequently wrong, and doesn’t use citations.
T. G. E. Powell. The Celts. Thames and Hudson: New York, 1980. Second ed; reprint. 1991. ISBN 0500272751. A basic overview of Celtic history, via cultural artifacts, Classical references, and medieval texts. This is somewhat dated in terms of current archaeology and approach, but the quality images and the background material regarding historic understanding of who and what the Celtic peoples and cultures were believed to be is still helpful.
Sjoestedt, M. L. Gods and Heroes of the Celts. 1949; translated by Myles Dillon. repr. Dover Publications, 2000. ISBN 0486414418 . A slim paperback, easy to read book, this is still considered a standard text, with some interesting observations. In some ways, Sjoestedt is a predecessor for the work of Rees and Rees, listed below. There’s much more to Sjoestedt than meets the eye; read carefully and thoughtfully. She makes complex things sound startlingly simple, and has many observations that are far more revelatory than you might think.
A Slightly More Advanced Starter Kit
Cross, Tom Peete and Clark Harris Slover. eds. Ancient Irish Tales. New York: Barnes and Noble Books, 1969; repr. 1988. ISBN 0389202541. This is the standard collection of medieval Irish literature in translation, and it includes the basic mythological tales, one version of the Tain, and samples of the heroic tales, dindsenchas, king cycles, and the other genres. Sadly, it’s now out of print.
Cunliffe, Barry. The Ancient Celts. Oxford: Oxford University Press, 1997; Penguin 2000. ISBN: 0140254226. I’ve posted a lengthy book review here. Cunliffe is one of the leading European archaeologists, and specializes in early Bronze and Iron age. Some of his linguistic data is a bit out of date, but he offers a thorough exploration of the various Celtic migrations and of Celtic culture and history pre-and post- Roman empire. A good bibliography, and excellent maps, with a useful chronology.
Green, Miranda J. Dictionary of Celtic Myth and Legend. New York: Thames and Hudson, 1992. ISBN: 0500279756. A very useful compendium that goes beyond myth and legend. I wish that she had been more careful about distinguishing her opinion from scholarly consensus and fact, but she does provide a useful bibliography. Green always has super photographs of artifacts and related images.
Brinley Rees and Alwyn Rees. Celtic Heritage: Ancient Tradition in Ireland and Wales. New York: Thames and Hudson, 1961; repr. 1989. ISBN 0500270392. A super introduction and overview of the mythological medieval Irish and Welsh literature, from a comparative (Dumezielian and occasionally quirky) point of view.