I have a number of books on folklore, mythical creatures and spirits and fairies. Hey, I like them. This is the best. This covers everywhere and everyone. It includes everything. As any good encyclopedia should, it runs A-Z. It prompts further reading. It links listings to others in the 'pedia and can prompt further research. It is at the back of the book that the information comes into its own.
It is all very well knowing the name of an entry, but what if you do not? What if you want a spirit to go with water, or a spring, or fate etc? Go to the back, they are all listed. But not just that. Want spirits associated with the creative arts? Corn and grain? Disease? They are all listed. Then look them up in the main 'pedia.
There is also none of the "maybe" and "could be" that you get with other publications. Carol Rose simply says how it is, or not. She states what is known, or not.
There are lists of Angels, Demons, tree spirits, and a list by Country of origin. Need an obscure Belgian fairy? You'll find it here.
There are some books that should be reprinted and massive sellers. This is one. Get it. It can be hard to find, but if you can just buy it.