There are a few things that every spinner should have on his or her book shelf. A book of spun samples. How to spin various kinds of yarns. And a book like this which introduces you to the wide world of fibers. The Fleece and Fiber Sourcebook primarily deals with an introductory, though mostly comprehensive, look at sheep wools. The sections at the end of the book discuss non-sheep fibers in a similar vein, those from goats, camelids, rabbits, and such. I am fairly well-versed in a few types of wool that I have used extensively over the years, but even I learned a few new things about those fibers from reading this book.
Most reference books aren't exciting to read (well, in a way they are), but I really found this book to be a page-turner. The first chapter introduces various useful terms, disambiguated the commercial world of wool from the that of the handspinner, and gave a quick zoological lesson about wool and the animals who make it. It is fully colorized, so each page has a picture of something, whether it's the raw/washed locks, sample swatches, and/or a picture of the cutie pie sheepies themselves. This is incredibly useful as we can associate the wool to the image of the breed of sheep (when applicable--not all breeds listed will have images of both animal and lock). It is nice to see how the samples turn out when you start with the raw lock.
The general format for each sheep breed is a blurb about the history of that breed, along with some interesting tidbits specific to that breed. There is information about fleece weight, fiber micron, dyeability, suggested spinning techniques, and advice about knitting/crocheting/weaving/felting. On occasion, there is an interesting story about a sheep or wool. For example, in the entry about Merino sheep, there is a cute story about the famous Shrek the Sheep.
The book starts off with the sheep breeds, which is primarily organized by sheep families. There are many sheep which don't fall into these categories, but may still have similar fleece qualities. Knowing the families of sheep will be useful in a plethora of ways as you educate yourself about how the different wools relate to one another.
When the book turns to other wool-producing animals, more than 2/3 of the way through the book, there is a mini introduction for that specific type of animal, whether its goats, camelids, or rabbits. Though these sections aren't as vast as the sheep section, there is a great deal of information here too (there just typically aren't as many breeds of angora as there are sheep, I suppose).
The Sourcebook is meant to be a quick reference since it doesn't delve into each breed for several pages--most will only have a dedicated 2-3 pages, some more, some far less. It makes up for depth with its breadth. It's a great starting point for your fiber study, and if you have only worked with a few handfuls of fibers, this reference book will be a boon companion.
My only criticism about this book is the lack of quick reference. There is a typical index in the back of the book, but it's time consuming to thumb through at a glance because it lists more than just the breed names. The table of contents is also difficult to search through if you don't immediately know how a fiber is categorized. I'll probably make a hand-written quick reference version so I can find a breed alphabetically instead.
For the price ($35 USD), it is a steal. You'll still need to experiment with fleeces on your own and build up your personal reference, but it's good to have on your shelf. Whether you're just getting started with spinning, need a refresher about a specific breed, or you need to identify some mystery wool, this book will be comprehensive enough for your needs.