The delineation of the order of the Bacillales is based on 16S sequence analysis and consists of the families of Bacillaceae (which contains the type genus), Alicyclobacillaceae (fam. nov., this volume), Listeriaceae (fam. nov., this volume), Paenibacillaceae (fam. nov., this volume), Pasteuriaceae, Planococcaceae, Sporolactobacillaceae (fam. nov., this volume), Staphylococcaceae (fam. nov., this volume), Thermoactinomycetaceae (Matsuo et al., 2006), and three family incertae sedis. Most of the family names were not validly published, but their allocation is in agreement with the phylogenetic outline given in this volume. One of the few general characteristics of the order is the formation of endospores that are formed in representatives of many genera of this order, although exceptions exist. Furthermore, the cell wall stains generally Gram-positive for young cells. The staining is supported by the chemical composition of the cell wall. If known, most genera allocated to the above families have menaquinone 7 (MK-7) although various exceptions are found, in particular amongst the Thermoactinomycetaceae where menaquinones ranging from MK-6 to MK-11 have been reported.

Type genus: Bacillus Cohn 1872, 174^AL.