Hypersaline environments are the principal habitats of petroleum deposition. They are also of intense evolutionary and ecological interest. This book presents a cross-disciplinary examination of the variety of halophilic microorganisms and their roles in modifying the ecology and geochemistry of hypersaline environments. The book also covers in detail the various inland and coastal habitats where halophilic microorganisms thrive. Geographically, hypersaline environments extend from the tropics to the poles, and from the terrestrial to the submarine. Organisms capable of living in such environments have faced unique evolutionary challenges.