The theory of heat treatment of steels, cast irons, non-ferrous metals and alloys is presented. Changes in structure and properties during quenching, tempering, aging, annealing with phase recrystallization, recrystallization and pre-recrystallization annealing, homogenization, annealing to reduce stresses, thermomechanical, chemical-thermal and other types of thermal treatment are analyzed. The textbook is designed for students specializing in metal science and heat treatment, as well as students of other metallurgical specialties and can be useful to engineers - metal scientists, thermists, casters, welders and metal workers.