This book which was written by Lei Shitai, the descendant of Mr. Sun Lutang, is the first monograph that systematically discusses the three kinds of martial arts within the Sun family, known as Neijia Quan. The author who has obtained the true essence of Neijia Quan due to the affinity with the Sun family now sincerely contributes it to world after sixty years of practicing and understanding. This book explains the profound in simple terms with a comprehensive study of varieties of theories of martial arts. The contents of the book include five parts: Sun-style Xingyi Quan, Sun-style Taiji Quan, Sun-style Bagua Quan (known as the Eight-Diagrams Quan), Sun-style Chunyang Sword and Discussions about Kung Fu and the virtue and skill in martial arts. A good mastery of the true essence of Neijia Quan means a combination of mind and body consistent and single-minded loyal to the virtue and skill in the martial art. The theory flowing like the surging river is never separated from the virtue and skill.