Various groups of microorganisms - bacteria, archaea, algae and even fungi - have adapted to a life in a hypersaline environment. Halophilic Microorganisms explores the many-fold aspects of life under these extreme conditions. Several contributions analyze the microbial communities in different hypersaline environments such as salterns, soda lakes, and the Dead Sea or salt sediments. Reviews of their biodiversity, phylogeny, and genetics are given as well as of the diverse adaptation strategies of salt-tolerant or salt-requiring microorganisms. Microorganisms that have adapted to moderate salt concentrations or to habitats with drastic fluctuations are also treated in addition to the extreme halophiles. Their physiological, biochemical and molecular mechanisms developed in response to salinity and high osmotic pressure as well as current and future biotechnological applications are presented.