One of my primary questions going into this book was, "What exactly is a demon?"
Bane's definition of demon appears to be "anything anyone has ever called a demon". Fallen angels, pagan gods, Japanese youkai, goetic demons and various mythological figures all make appearances. The Encyclopedia of Demons in World Religions and cultures has thousands of entries that span several different cultures.
Entries include the name (and variations) of the demon and some mention of where it comes from (its culture, religion, grimoire, et cetera). Where possible, physical descriptions of the demon, and information on its behavior are also included. Some demons, especially those from goetic grimoires, also have information on what they might be summoned for or how they interact with people. Unfortunately, there are no pictures or illustrations.
Each entry is individually sourced (often including the relevant page numbers), which I really liked. I'm not very familiar with demons and demonology, and so I can't say with any authority how accurate these entries are. I can, however, check the sources given, both in the entries and in the extensive bibliography.
I wouldn't suggest this book as the only reference one would need (I'd be hesitant to suggest any single book for that), but I do think it's a good place to start. It's very helpful if you need to get a brief overview of a demon, and an idea of where to look for further research.
Note: I received a free copy of this book through the LibraryThing Early Reviewers program. This has no bearing on the content of my review.

A great reference book for all things daemonic. I teach classes that address monsters and supernatural beings around the world and throughout history. I now refer my students to this invaluable text when they need to do research.

A great reference for those interested in such things. Just yesterday I was reading a novel and came across a name that I was able to look up and get satisfactory information about. There are two things in particular I like about this book -- the straightforward writing and the sources added to each entry. There's also a lengthy bibliography, which I always enjoy. One criticism, however, is that this reads more like a dictionary than an encyclopedia. The author was deliberately brief in order to cover a large number of entries, so each entry is concise and introductory. Still, this will be a useful addition to my reference materials. Just remember, though, that this book is a first stop in research, not the last. ( )

Theresa Bane's _Encyclopedia of Demons in World Religions and Cultures_ is a more than adequate introductory text on the subject of world demonology. Bane presents in the introduction her conception of "demon", and despite using the Latin "daemon" for the Greek "daimon," is very useful in understanding how she presents the various spirits in the "Encyclopedia." This is important as many of the spirits, especially those from non Abrahamically influenced cultures, do not always fit Western culture's various understandings of the term. The book also boasts, and delivers on, a lengthy bibliography. While the "Encyclopedia" is heavy on Abrahamic and grimoire-derived demons, it includes spirits from a host of other cultures as well. Perhaps its greatest flaw is that it calls itself an encyclopedia when it is at best a dictionary.

An Early Reviewer win.
This is an excellent book with a huge bibliography and many sources. And while I sat down and read it through beginning to end, as a reference book, that's not the best way to look at it/use it.
It did, however, have the added benefit of keeping some people from sitting next to me on the bus.
I've also become entirely intrigued by Bensozia thanks to this book. I'm going to have to read Ecstasies by Carlo Ginsburg and reread Montaillou by LaDurie because I discovered she's mentioned in those books as well. (I hadn't recalled her in Montaillou, but I read that nearly 30 years ago.)
I discovered there are numerous demons of migraines, which doesn't shock me, and a demon of Morris dancing, which sent me into a laughing fit (I used to be a Morris dancer).
I had never heard about an association of Eostre with Lilith. I simply can't comprehend that one. Eostre was a Germanic pagan goddess who later gave her name to the holiday Easter. Unless the demonic association is simply because she's a pagan goddess, I can't see how the two would be related. Granted, I didn't go through the bibliography to look for a source because it's so huge. And I don't believe the author created this idea herself--I'm sure the documentation is there. It just struck me as strange.
The only quibbles I had with this book are things most readers wouldn't even notice. It was just weird things that happened in the styling of the book that I notice simply because I can't leave my job behind when I read a book (I'm a production editor, so I look for those kind of things to make sure they don't happen).
If you need a research/reference books on demons from not just one religion but many, this is definitely the book for you. ( )