AbstractSevere plastic deformation (SPD) can lead to emergence of microstructural features and properties in materials which are fundamentally different from the ones well known for conventional cold deformation. In particular, the instances of unusual phase transformations resulting in development of highly metastable states associated with formation of supersaturated solid solutions, disordering or amorphization and their further decomposition during heating, high thermal stability of the SPD‐produced nanostructures, and the paradox of strength and ductility in some SPD‐processed metals and alloys are discussed.