A charming little companion to the Matthews' deck of the same name, accessible whether you are new to their brand of Celtic/Arthurian scholarship or not, although a grounding in the Arthurian traditions as well of course as in Tarot is recommended. There are newer editions available, which might be better if you don't already have a copy (probably bought this one in the early 90s; it's a 1990 edition) as they are active scholars and always updating their vision.