Market: Research scientists and students in materials science, physical metallurgy, and solid state physics. This detailed monograph presents the theory of reversible plasticity as a new direction of development in crystal physics. It features a unique integration of traditional concepts and new studies of high- temperature superconductors, plus in-depth analyses of various related phenomena. Among the topics discussed are elastic twinning (discovered by Dr. Garber), thermoelastic martensite transformation, superelasticity, shape memory effects, the domain structure of ferroelastics, and elastic aftereffect. Partial Contents: 1. Transformation of Dislocations. Dislocation Description of a Phase Transformation Front. 2. Dislocation Theory of Elastic Twinning. Twinning of Crystals: Principal Definitions. 3. Statics and Dynamics of Elastic Twinning. Discovery of Elastic Twinning. Verification of the Validity of the Static Theory in a Description of the Macroscopic Behavior of an Elastic Twin. 4. Thermoelastic Martensitic Transformation. Martensitic Transformation: a Diffusionless Process of Rebuilding the Crystal Lattice. 5. Superelasticity and the Shape Memory Effect. Main Characteristics of Superelasticity and Shape Memory Effects. 6. Reversible Plasticity of Ferroelastics. Ferroelastics: Main Definitions. 7. Investigation of Reversible Plasticity of Crystals by the Acoustic Emission Method. Emission of Sound by Moving Dislocations andTheir Pileups. Methods Used in Experimental Investigations of the Acoustic Emission Generated by a SingleTwin. Acoustic Emission Associated with Elastic Twinning. 8. Influence of Reversible Plasticity of Superconductors on Their Physical Properties. Reversible Changes in the Parameters of Traditional Superconductors under the Action of Elastic Stresses. Influence of Magnetic Fields on Reversible Changes in the Parameters