I've had this listed as "reading" for a long time now, but truthfully I've read through the entire thing. I just keep going back to it for ideas on new training exercises, or for help with fixing problems and sharpening up skills.
This is a great resource that spans levels of training from green to finished. As a rider that's new to reining on a horse that's finished (but who has had a lot of time away from being asked to work and therefore needs sharpening up), I've found this book extremely helpful in understanding the fundamentals of reining and learning how to build on those fundamentals to refine my skills in each area of the discipline.