Includes a description of the Gammaproteobacteria (1203 pages, 222 figures, and 300 tables). This large taxon includes many well known medically and environmentally important groups. Especially notable are the Enterobacteriaceae, Aeromonas, Beggiatoa, Chromatium, Legionella, Nitrococcus, Oceanospirillum, Pseudomonas, Rickettsiella, Vibrio, Xanthomonas and 155 additional genera.