Don Riso is one of the key figures and innovators in the field of Enneagram studies. This is not the first of his books (and here he has partnered with Russ Hudson), nor is it the most recent, but it does represent refinement and improvement over his earlier works. There are several other authors who have written books on the Enneagram, but I don't think anyone else has done it as well. Riso is a highly articulate guy who doesn't sugar coat things, and reading his descriptions of personality types such as the average or unhealthy three is a bit unsettling. I'd say he has, for better or worse, great insight into human nature. A minor criticism is that I disagree with his classification of certain famous people, although in most cases he seems to get it right. Anyone interested in personality and human behavior in general will find this a fascinating read. Author of Adjust Your Brain: A Practical Theory for Maximizing Mental Health.