This book is simply fantastic. The whole series is excellent. It has clear, well organized, well thought out lessons that are instantly understandable and that cover exactly what you need to know. It is an indispensable companion to the usual high school geometry textbook. If the textbook isn't clear or complete, this solves the problem. The book was obviously written by someone (or some people) who not only know geometry, but also know how people learn, what high school students need to know, and common problems they will have in their learning of the subject.I don't mean to go on, but I have looked at A LOT of geometry textbooks and have taught the subject a good bit, and if I had to only use one book this would be it. You can get this used for on Amazon for $3 or $4, and it's simply the deal of a lifetime.