Abstract
This chapter describes hypersaline environments and the diversity of life living in them. It explores the factors influencing diversity, community composition and distribution of halophilic microorganisms, as well as their mechanisms of adaptation to high salinity. The chapter also discusses the ecological guilds and biochemical groups of halophiles, and presents the results of six case studies on hypersaline environments including thalassohaline coastal salterns, inland salt lakes, the Dead Sea, and alkaline soda lakes. The chapter concludes with an account of the importance of hypersaline environments and halophiles to the society.