This book provides a complete description of hydrogen technologies from the basic theoretical underpinnings to the different production routes for various applications. It summarizes the most recent research findings with respect to theory and the broad array of industrial technologies currently in place as well as those under development with high potential. Special attention is given to the hydrogen embrittlement mechanisms at room and high temperatures as well as problems related to hydrogen in liquid and high-pressure compressed states. The author further describes the hydrogen diffusion embrittlement issues related to different types of metallic materials from steel to light alloys to nikel-based superalloys.