This volume includes numerous introductory chapters on the basic concepts and practice of prokaryotic taxonomy in addition to detailed descriptions of the Archaea, phototrophic bacteria and some very deep bacterial phyla. Introductory chapters include the topics of classification of prokaryotes, the concept of bacterial speciation, numerical and polyphasic taxonomy, bacterial nomenclature and the etymology of prokaryotic names, nucleic acid probes and their application in environmental microbiology, culture collections, and the intellectual property of prokaryotes. The first Road Map to the prokaryotes is included as well as an overview of the phylogenetic backbone and taxonomic framework for prokaryotic systematics. This volume also provides descriptions of 413 species in 165 genera that are assigned to the phyla Crenarchaeota, Euryarchaeota, Aquificae, Thermatogae, Thermodesulfobacteria, Deinococcus-Thermus, Chrysiogenetes, Chloroflexi, Thermomicrobia, Nitrospira, Deferribacteres, Cyanobacteria, and Chlorobi. In addition, the volume contains an introductory chapter to nonoxygenic, phototropic species of Bacteria belonging to the Proteobacteria and Firmicutes, which will be repeated in more detail in subsequent volumes.