This book is intended as a general reference manual for persons engaged in or concerned with the practice of space medicine. A large body of ground-based research, including both human and animal experimentation, and inflight life sciences accomplishments support the findings presented in this book. Space medicine is a relatively new field of environmental medicine dealing with the unique aspects of health maintenance and care of individuals exposed to the rigors of space. The sustenance of life in space and the practice of medicine require a team approach and draw upon the knowledge of many areas of engineering, human factors, and medical specialties. Current activities of physicians and life scientists are devoted mainly to achieving a better understanding of the physiological changes which result from weightlessness and the development of procedures and countermeasures to facilitate the transition to space and to assure a safe return to Earth. The domain of space is used at this time by a small number of highly select and healthy individuals, with the practice of space medicine focusing on preflight prevention of disease. As space activities expand, a larger and more diversified population will be involved in a variety of activities in the weightlessness of space. At this time, medical professionals and the practice of medicine also will move into space. This next milestone will produce a quantum advance in our understanding of human adaptation to the weightless environment and, at the same time, will require development of new therapeutic means and procedures not dependent on gravity. Space medicine will continue to grow and will become a well-established medical specialty.