This book gives an insight in the development of internal energy and strength and how it may be developed in the proper study of Tai Chi Chuan, after extensive training and study of the martial art.
This is a very informative book but it is not primarily a manual on how to do Qigong. It is a work that explains the history of the development of Qigong, it's relationships to Tai Chi Chuan, and many other fascinating relationships, applications, and observations.
There is approximately 1/3 of the book devoted to how to do Yang style Tai Chi Qigong. A vastly superior instructive tool for the same ideas for me was his DVD "Simple Qigong Exercises for Back Pain Relief."