The monograph summarizes the literature data and the author’s results concerned with the physiology and biotechnology of chemolithautotrophic hydrogen-reducing organisms. A general notion is given about the area of distribution, systematics and metabolism of hydrogen-reducing microorganisms (hydrogen bacteria and carboxydobacteria).The monograph describes the methods and equipment for microorganism cultivation on gas substrate. The author summarizes the results obtained by her during many years of investigation aimed at revealing of the growth mechanisms and metabolism of hydrogen-reducing microorganisms depending on the availability of energy and carbon sources, conditions of mineral nutrition and physical-chemical environmental parameters. The following biotechnological aspects of hydrogen-based biosynthesis are presented: the prospects of using hydrogen-reducing bacteria as a bioregenerative link in human life support systems; the results of development and operation of pilot production of hydrogen-reducing bacterial biomass and the results of bioavailability tests as a source of protein in in vitro and in vivo experiments; the results of synthesis of biodegradable plastics polyoxyalkanoates and possibilities of using industrial sources of hydrogen. The monograph considers the prospects of hydrogen energetics as the basis of hydrogen-based biosynthesis development.