This book is a comparative review of spin electronics ("spintronics") research and development activities in the United States, Japan, and Western Europe conducted by a panel of leading U.S. experts in the field. It covers materials, fabrication and characterization of magnetic nanostructures, magnetism and spin control in magnetic nanostructures, magneto-optical properties of semiconductors, and magneto electronics and devices. Spin Electronics is unique in that it combines tutorial and introductory information on the significance of spin electronics research and applications development in this rapidly developing field. It reviews profound technical and policy implications of spin-based devices for the future of semiconductor electronics, non-volatile computer memory, nanotechnology, and quantum computing and communications. For example, the report discusses the potential for spin electronics to help maintain the progress in price and performance of electronics and computers described in Moore's Law. Finally, information on funding and level of effort in the laboratories visited by the panel is provided.