Book excerpt: Providing a broad historical perspective, this book explores the interactions between humans, microorganisms, and plants in a closed habitat, and the life support systems necessary to maintain habitability over long periods of time. Topics include the cultivation of bacteria, microalgae and higher plants; the use of biotechnology to support life outside the Earth's biosphere; methods for recycling air, water and food for human consumption; interactions between humans and other organisms in CMESs; and methods for intensifying the level of photosynthesis. In addition to space the authors investigate problems associated with living conditions in dangerous or difficult environmental areas on Earth such as the Arctic and Antarctica, deserts and mountains.