Several different nomenclatures have been applied to the Clostridium difficile toxins and their associated genes. This paper summarizes the new nomenclature that has been agreed to by the research groups currently active in the field. The revised nomenclature includes C. difficile toxins and other related large clostridial toxins produced by Clostridium sordellii and Clostridium novyi, and corresponding toxin genes, as well as toxin production types of C. difficile strains.