The anaerobic Gram‐negative bacteria are part of the microbiota of the oral cavity, gastrointestinal tract, and urogenital tract. Many taxonomic changes have been instituted based on newer biochemical and molecular sequencing considerations. Many of the bile‐sensitive species of Gram‐negative bacilli, such as
Prevotella
and
Porphyromonas spp.
, make up a large percentage of the normal microbiota in the oral cavity and are involved in many different types of oral infections. The pigmented anaerobic Gram‐negative bacilli include members of the genera
Prevotella
,
Porphyromonas
, and
Alistipes
. The chapter includes a few additional Gram‐negative rods of human pathogenicity. It also helps the laboratory staff to perform all analyses, including appropriate quality control recommendations, from the receipt of the specimen (anaerobic Gram‐negative bacilli) through processing, testing, interpretation, presentation of the final report, and subsequent consultation.