Bacilli is a taxonomic class of bacteria that includes two orders, Bacillales and Lactobacillales, which contain several well-known pathogens such as Bacillus anthracis (the cause of anthrax).

The name Bacilli, capitalized but not italicized, can also refer to a less specific taxonomic group of bacteria that includes two orders, one of which contains the genus Bacillus.

The word "bacillus" (or its plural "bacilli", with a small b) is also a generic term to describe the morphology of any rod-shaped bacterium.

The currently accepted taxonomy based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)[2] and the National Center for Biotechnology Information (NCBI).

[3] Pasteuriaceae "Kyrpidiaceae" "Effusibacillaceae" "Tumebacillaceae" "Acidibacillaceae" Alicyclobacillaceae "Desulfuribacillaceae" "Calditerricolaceae" "Bacillus thermozeamaize" {Bacillales_F: Bacillaceae_M} "Thermicanaceae" "Brockiaceae" Novibacillaceae "Polycladomycesaceae" "Planifilaceae" Mechercharimyces {JANTPT01} "Desmosporaceae" Thermoactinomycetaceae Microaerobacter {DSM-22679} "Tepidibacillaceae" "Reconcilibacillaceae" "Xylanibacillaceae"