This is a very basic introduction to bits and their function. The book never adequately addresses the subject and comes far short of the title. I believe that all except the most novice of horse enthusiasts will already be familiar with the vast majority of the material presented.
If you have absolutely no knowledge of the subject and you're looking for a very brief overview, this is the book for you.
"The Complete Book of Bits and Bitting" provides a much more thorough coverage of the subject although it is perhaps a bit too thorough for the novice rider.