Strains of Clostridium difficile produce a number of surface-localized proteins, including the S-layer proteins (SLPs) and other proteins that have suspected roles in pathogenesis. During the Third International C. difficile Symposium (Bled, Slovenia, September 2010) discussions were held on standardization of nomenclature. Gene designations were proposed for the large family of cell wall proteins that are paralogues of the SLP and contain putative cell wall binding motifs. This paper summarizes the agreed nomenclature, which we hope will be used by research groups currently active in the field.