The halophilic Archaea (Class Halobacteria) represent a physiologically and phylogenetically distinct lineage within the archaeal phylum Euryarchaeota. Members of Halobacteria are encountered in a wide range of environments where their absolute requirement for salt is satisfied, where they play an important role in bioremediation and carbon turnover. While the diversity of halophilic archaea has been extensively examined using culture-dependent and independent approaches, ecological and physiological patterns governing the observed patterns of diversity remain obscure. Here, I summarize research conducted in my laboratory during the last decade aimed at understanding global patterns of archaeal diversity. Our results document the occurrence and high levels of phylogenetic diversity of halophilic archaea in low salinity/fluctuating salinity habitats, discovery and characterization of novel genera from such ecosystems, and demonstration of the wide utilization of trehalose/2-sulfotrehalose biosynthesis as an osmoadaptive mechanism within the Halobacteria.