The Essence and Applications of Taijiquan, which was written by Yang Chengfu, was published in 1923, but despite its importance for taiji practitioners in the west, it was available only in Chinese. I knew about it because my taiji`s master; Dr. Qi Ke Bao, used it as one of his main sources for studying and, of course, teaching it. This book is for advance students who already are acquainted with Yang style long forms and with pushing hands exercises. The emphasis of the author is in functional features and in applications. It is written, as the translator points out, as "demonstration narrative"; when I was reading it, I felt as if receiving specific instructions for the important points in each movement. I think that the translation is precise and that Louis Swaim, the translator, was able to make Yang Chengfu`s ideas accessible to an English reader (Qi Tiang Shu, my master`s son and a Taiji master himself compared some random paragraphs with the original Chinese version and concluded that the translation kept the original sense). I found the translator's comments appropriate and very useful. He explains the meaning of some words, which are difficult to grasp, in such a way that they become more intelligible for a western reader. I think that for someone interested in Taiji, mainly in Yang style, the reading of this book is as necessary as the reading of the Taiji Classics.

I have only been taking Yang Style TaiJi 108 form classes for 8 months now. This book reinforces the basics and fundamentals that I have been repeatedly taught all this time. But the book goes beyond that because it helps me to visualize the "opponent" against whom the form is applied.
I highly recommend the book to Yang Style TaiJi students who already have taken classes under a coach who teaches and stresses the need for a solid foundation in form; e.g., upright posture, breathing to the dantien, relax the shoulders and sink the elbows, etc.