This has to be one of the ultimate books for handspinners who want to know about what they're doing, why it's working, and the fibers and gadgets they use.
While it's not current on some of the newer fibers and resulting "art" yarns, it's a solid foundation for a lot that came before. Highly recommended for those who spin, or those that want to raise fibery plants or animals.
If you're looking for a book to teach you handspinning this isn't the title. However if you're looking for a reference book to tell you all about different things about spinning then this is pretty clear. It's got a lot of detail and illustrations and is clearly illustrated.
An encyclopedia is simply not a useful form for a book on handspinning, unless it is truly exhaustive, which this is not. Nonetheless, a thorough reading of this book will probably have the reader picking up some interesting tidbits which are not common in other books.