A new method of identifying bacteria, phylogenetic 16S rRNA sequencing, has led to major reorganizations among most genera of anaerobic bacteria. The pigmented Prevotella species now comprise seven species including P. nigrescens and P. tannerae; P. intermedia/P. nigrescens-like organisms await inclusion. The former Mitsuokella dentalis and Hallella seregens were transferred to Prevotella as one species, P. dentalis. P. enoeca is a new nonpigmenting Prevotella. The genus Porphyromonas currently includes 11 pigmented species and one nonpigmented species, P. catoniae; P. levii-like and P. endodontalis-like organisms are candidates for the genus. Fusobacterium nucleatum currently has five subspecies, and F. varium includes the former F. pseudonecrophorum. Former Wolinella recta and Wolinella curva now are Campylobacter rectus and Campylobacter curvus; Campylobacter showae is a new species. Isolates included in the bile-sensitive former Bacteroides gracilis now are Campylobacter gracilis; the bile-resistant B. gracilis isolates were transferred to a new genus, Sutterella, as S. wadsworthensis. The new Actinomyces species include two subspecies of the A. neuii and the A. radingae-A. turicensis complex. The genus Eubacterium sensu stricto is represented by E. limosum, and the former E. alactolyticum was reclassified in a new genus, Pseudoramibacter, as P. alactolyticus. Recent entries include E. saphenum, E. minutum, E. exiguum, E. infirmum, and E. tardum. A new genus, Atopobium houses some former lactobacilli and streptococci. The genus Peptostreptococcus also have four new species; P. hydrogenalis, P. lacrimalis, P. lactolyticus, and P. vaginalis.