The subject of the book is heat and cold storage with PCM (phase change material). Currently there are plenty of publications in journals on different aspects of PCM technology, but there is no introduction into basics and applications available for a beginner or for somebody who works in one aspect of PCM technology and wants to get a general overview. The book is intended to fill this gap for researchers, graduate, and PhD students, mainly within science and engineering. The book summarizes and explains the most important basics and applications in a single text. The focus is on the explanation of general concepts and their discussion on selected examples. To go beyond an introduction, each chapter supplies many references with focus on such references that serve as an introduction into a special aspect, interesting websites, and other similar information. The book also contains many derivations of basic equations, examples, graphs and tables. To make reading easier, the appendix also includes a list of the most important definitions. As an introduction, the chapters cover all aspects starting from basic theoretical background to materials analysis and modification, storage design, storage integration, and different application examples. Special focus is on applications in buildings, because this is where the potential to apply PCM is very high.