This book provides a comprehensive account of the current status of molecular hydrogen medicine, a young field that emerged with the discovery that inhalation of hydrogen gas leads to the elimination of harmful reactive oxygen species in rats. Various physiologic effects have since been demonstrated, and possible medical applications identified. Numerous clinical projects have now been undertaken, yielding startling results. Despite this, molecular hydrogen medicine remains underappreciated among the medical community at large. The author aims to rectify this situation by fairly but critically evaluating the potential clinical benefits based on the latest scientific research. In addition, the observed physiological effects of hydrogen gas are considered within the broad context of the evolution of life on earth, offering new perspectives and helping to place molecular hydrogen medicine legitimately within the framework of life sciences. Written in an accessible manner, the book will be of value to students, researchers, clinicians, and the general public.