Many global environmental issues are being vigorously discussed these days, particularly the topic of reducing CO2, which is caused by the consumption of fossil fuels. Given the trends in contemporary power consumption in Japan, which have a lot to do with the emission of CO2, you will notice a less well known fact: that approximately 30% of power consumed is due to the demand for cooling (air-conditioning). Thus, air-conditioning engineers are now required to carry out an important task in the prevention of global warming by further promoting energy savings in air-conditioning technology. This book describes thermal storage technologies, which is one of the important energy saving approaches involved in air-conditioning, and outlines every aspect of thermal storage beginning with the current global environment, the history of thermal storage systems and principles of heat pumps, up to concepts and design methods of water and ice thermal storage systems. One of the benefits of this book is its easy-to-understand descriptions featuring diverse illustrations and charts and, so to speak, its thematic self-contained chapters. The book will be a helpful guide for people wanting to learn more about thermal storage technology, which is often considered to be "difficult to understand" or "too complex" despite its long history. This book was written mainly for junior building equipment engineers and equipment engineering students.