Xing Yi Quan Xue (The Study of Xing Yi Quan) was written by Sun Lutang in 1915.
This book gives clear instructions not only in the basics of Xing Yi Quan and the important principles for beginners, but also clearly teaches and illustrates the major forms of the style including the Five Elements, Wu Xing Lian Huan Quan, the 12 Animals, Za Shi Chui, as well as the paired practice routines of the Five Elements and An Shen Pao.
Sun Lutang mastered all three internal styles of Chinese Boxing: Taiji Quan, Bagua Quan, and Xing Yi Quan. His teachers included: Guo Yunshen (Xing Yi Quan), Cheng Tinghua (Bagua Quan), and Hao Weichen (Taiji Quan). Later in life he founded his own style of Taiji: Sun style Taiji Quan.