This book provides a descriptive classification of the various concepts, giving characteristic performance data and design fundamentals. Systems based on sensible heat storage, latent heat storage and thermo-chemical processes are presented, including the state of maturity and innovative solutions. Essential for the effective integration of thermal storage systems is the optimal adaption to the specific requirements of an application. This is shown in the second part, where storage solutions for conventional and solar thermal power plants are described. Further examples show the integration into batch processes, mobile applications or options to support the utilization of waste heat. Systems using thermal energy storage for facility scale storage of electricity are also described. Storage systems for medium and high temperatures are an emerging option to improve the energy efficiency of power plants and industrial facilities. Reflecting the wide area of applications in the temperature range from 100 °C to 1200 °C, a large number of storage concepts has been developed.