Phase change material technology is one of the emerging technologies nowadays. At present, the technology is mainly utilized for thermal energy storage, cold chain applications, and electronics cooling. However, there are many more areas where the use of this technology would be beneficiary. Phase change material technology could enhance thermal protection of protective garments and regulate the heat transfer through roofing systems making buildings more energy efficient. These applications and others are discussed in the book. To apply the phase change material technology successfully, some design requirements need to be considered which are revealed in the book for the first time. The book provides guidance and tools for designers and engineers involved in the development of products utilizing this technology. In addition, procedures for testing the thermal performance of products equipped with phase change material are introduced and discussed. Due to the advanced knowledge presented in the book, it will also be a valuable reference text for researchers in academia as well as students in material science.