This book describes the most hostile habitats of our environment and their most hardened inhabitants. The survival strategies which these so-called extremophiles have developed are analyzed in a way accessible to the lay reader but still in touch with the latest research news, including for instance, research on heat-shock proteins and genome sequencing. Michael Gross describes the significance of extremophiles and extreme conditions for biotechnology, medicine, and research into the origin and early evolution of life. Finally, the book takes us into space to explore the possibility of life on other planets including Mars, and the search for habitable planets in other solar systems.