Materials with metastable structures and microstructures have been used with success to create unusual structural and functional properties and property combinations. Highly nonequilibrium technologies for creating metastable materials have been devised which allow materials to be prepared far away from the thermodynamic equilibrium. Using these methods, materials can now be designed to possess specific properties tailored to fit an application, rather than fitting an application to the properties of available materials. However, as these materials are metastable with respect to structural and compositional changes under temperature, there is great concern for understanding and controlling their limitations. This book features both fundamental as well as applied aspects of the subject by stressing the structure/property relationships, the conditions for stability of these materials, and the requirements for technological applications. In addition to the synthesis, processing, characterization, properties, and applications of such materials, attention is also focused on the modelling of structures, phenomena and processes. Topics include: synthesis and processing; thermodynamic and kinetics; phase transformations and properties and applications.