Structure and dislocation substructure formation in the course of plastic deformation of crystalline materials is determined in the first instance by the temperature and the degree of deformation. Hot, warm and cold deformation are distinguished. An approach to the definition of hot, warm and cold deformation has to be developed not in connection with the necessity of heating or cooling, but on the basis of structural changes in the deformation process. The correlation between processing, structure, dislocation substructure and mechanical properties and the physical nature of typical defects that appear after severe plastic deformation (splitting and 45degrees-embrittleness) are discussed.