This chapter deals with a practical system for identifying members of the genus Pseudomonas. In diagnostic microbiology, laboratory identification of pseudomonads and other glucose nonfermenting bacteria is based on phenotypic characters including morphological, physiological, and nutritional attributes. The chapter summarizes materials and methods for identification of glucose nonfermenting Gram-negative bacteria. P. aeruginosa has a single polar flagellum, but a few atrichous strains have been encountered. Strains may contain cells with no flagella or more than one flagellum. Other glucose nonfermenting Gram-negative bacteria display similar reactions on these media and, hence, must be differentiated from pseudomonads. The genus Xanthomonas was created to group together the yellow-pigmented, phytopathogenic pseudomonads. The taxonomic validity of Pseudomonas denitrificans has been questioned by Doudoroff and associates. Phenotypic characterization and deoxyribonucleic acid and ribosomal ribonucleic acid homology studies on strains designated P. denitrificans indicate that these strains belong to other recognized species and genera.