I don't normally write about books I can't wholeheartedly recommend, but I read The Handknitter's Yarn Guide: A Visual Reference to Yarns and Fibers and I just wanted to mention some pros and cons of this book.
I think the cons could outweigh the value of this book to everyone but expert knitters. This is unfortunate, because most expert knitters will find the information in this book to be superflous. They will know it already. But, if you really like lovely photographs of simple swatches, this would be a good book to check out.
Opening section talks about swatching, and different needle sizes for different fabric results.
Burn tests for some fibers are mentioned and described clearly.
Gauge and yardage suggestions are offered for yarns described*.
Short descriptions of the origins and uses are offered for each type of fiber mentioned.
Fibers that don't often get great coverage in yarn books, like Rayon, Tencel, and camel are covered. Rare fibers like Kenaf, seacell, nettle, possum, and bison are mentioned briefly among a list of 10 "Rare and Curious" fibers.
Tables in the back make comparisons between American, European and Australian systems of yarn weights, needle sizes, knitting terms, and measurement conversions. These might be very helpful sometimes.
Yarn labels, including care instructions and symbols, are demystified very well.
There is no discussion of washing and dressing swatches.
The book conflates ply count with yarn thickness (more plies = thicker yarn.) THIS IS NOT TRUE. I'm sorry, it's just not.
*but good luck figuring out which 12-ply Bulky Camel yarn they mean. They don't list exactly which yarns are used for each sample.
Overall, I recommend The Knitter's Book of Yarn. It will get you farther and be more worth your while than this book.