The limitations of fossil fuel supply and the need for decarbonization of energy systems presage the dawn of the hydrogen economy. However, realizing this vision will require developing and implementing solutions to engineering and technology challenges in hydrogen production, storage, utilization and distribution. "Hydrogen: Science, Engineering, and Energy Systems" presents a comprehensive overview of these issues. Hydrogen production alternatives are examined and the competing options analyzed on the basis of fundamental scientific principles. Similar discussions are included on other aspects of the hydrogen economy, not only answering questions of "how" and "what", but also explaining the observed phenomena by seeking answers to questions of "why" through an understanding of the basic properties of hydrogen. This discussion is integrated with societal energy needs and demands, to enhance an understanding of the place of hydrogen in energy systems.