This book on the conception, development and application of metallic materials with high specific strength and high specific stiffness, or high structural efficiency, encompasses the scientific foundation necessary to control properties through control of composition, processing and microstructure, and also addresses the current state of the development of such materials as well as the conception of new metallic materials with high structural efficiency. The dominant emphasis is on aerospace applications. A number of new developments are presented, including information on titanium alloys modified with boron and silicon to provide dramatic improvements in strength and stiffness, and new aluminium alloys strengthened with quasi-crystalline precipitates for good high temperature properties. There is also an extensive update on sever plastic deformation and on nanocrystalline metals for structural applications.