Shosui Fukuyama was a police officer in the region known as Koga, one of the centers of ancient ninjutsu. To do his job better, he researched the ancient art, consulting with families in the area and studying the old texts such as the Bansenshukai.In the 1950s, he put out this book on the modern applications possible with the art. He quotes ancient texts and examines ways the principles can still be used in the modern world.Many of the tools are obsolete, but the strategies and tactics for stealth, manipulating people and related skills are timeless.The purpose the author had was to make the art of ninjutsu alive throughout the ages. His personal experience in using much of the skills in the book insures that what is written will withstand the test of time.