This book was written based on three studies already published by the author: , and . To publish this work, the author reviewed important documents about Youshin-ryu Jujutsu and TenjinShinyou- ryu Jujutsu which are roots of Kodokan Judo and which are spread to the world nowadays. The author is confident that this book could be the first one which shows the spirits of Japanese Jujutsu clearly.