Methods and the latest results of experimental studies of the strength properties, polymorphism and metastable states of materials and substances with extremely short durations of shock-wave action are presented. The author provides a comprehensive and theoretical description of specific features of the dynamics of elastoplastic shock compression waves in relaxing media. The presentation is preceded by a detailed description of the theoretical foundations of the method and a brief discussion of the basic methods of generating and diagnosing shock waves in solids. Key Selling Features: Addresses dynamic elastic-plastic response, spallation, and shock-induced phase transformation. Provides a centralized presentation of topics of interest to the shock physics community Presents new data on the mechanism and basic patterns of sub-microsecond polymorphic transformations and phase transitions. Investigates destruction waves in shock-compressed glasses. Analyzes the behavior of highly hard brittle materials under shock-wave loading and ways to diagnose fracture.