In the last decade after the discovery of "giant magnetoresistance effects" in me tallic multilayers worldwide developments in basic research and in engineering applications have been achieved, and various remarkable results have been ob tained in both fields. On the basic research into the GMR effects an excellent re view book edited by Hartmann was published in 1999, entitled "Magnetic Multi layers and Giant Magnetoresistance", and it describes the experimental and theoretical aspects of GMR studies and the magneto-optics in metallic multilayers, including applications in electronic data storage fields. This book aims to give an overview on the electronics applications of the GMR in metallic multilayers, espe cially on the sensors and memories in magnetic data storage, the main concerns of electronic engineers. If the mean free path of conduction electrons is longer than the period of the multilayer, and for a low applied magnetic field magnetizations in the adjacent magnetic layers are in antiparallel, the GMR effect in magnetic metallic multilay ers occurs due to the resistance change in the electric current flowing in the layer plain, with a change in the magnetization from antiparallel to parallel alignment by an applied magnetic field (CIP mode), i. e. , in the saturation field magnetiza tions are in parallel and the resistance is lowered. The saturation field H, is given by the RKKY-like magnetic coupling between adjacent magnetic layers through a nonmagnetic conductive layer between the layers.