This book is a collection of papers on a fundamentally new concept in physics — the photon's magnetic field, B_π. It discusses various applications of B_π to predict the existence of new magneto-optic phenomena and to reinterpret some of the fundamentals of optics in terms of B_π of the photon. One of these new phenomena, optical NMR spectroscopy, has already been verified experimentally, leading to a new analytical technique of widespread potential utility.