Artificially structured materials granular magnetic solids, as well as nano-sized multi-layer films are of great interest. The granules consist of nanometer sized metal particles embedded in an immiscible medium, in most cases an insulator. The nano-structured composites are known to exhibit peculiar magnetic properties, offering valuable applications in material science. A number of MLs or compositionally modulated magnetic films have been actively investigated for the purpose of developing new materials with superior characteristics or new functions such as a perpendicular magnetisation, soft magnetism, or spin-flopping at low field. This book presents and reviews research in the study of insulating granular magnetic materials.