Book excerpt: All atomic particles have a particular "spin." Simple as spin may sound, the quantum mechanical reality underlying it is complex and still poorly understood. Because of the wide range of physics needed for its understanding, spin is not described in sufficient depth by any standard textbook. Yet this mysterious quality and the statistics associated with it have vast practical importance to topics as wide-ranging as the stability of atoms and stars and magnetic resonance imaging. Originally published in 1974, Sin-itiro Tomonaga's The Story of Spin remains the most complete and accessible treatment of the subject, and is now available for the first time in English translation. Tomonaga tells the tale of the pioneers of physics and their difficult journey toward an understanding of the nature of spin and its relationship to statistics.