Clostridioides difficile infection (CDI) is the primary cause of hospital-acquired diarrhea and pseudomembranous colitis. CDI is dependent on the secretion of one or more AB-type toxins: toxin A (TcdA), toxin B (TcdB), and the C. difficile transferase toxin (CDT, or binary toxin). While TcdA and TcdB are considered the primary virulence factors, multiple studies suggest that CDT increases the severity of CDI. CDT belongs to the Iota family of binary toxins and consists of two proteins: an ADP-ribosyltransferase (CdtA) and a cell binding and pore-forming protein (CdtB). CdtB engages host cells by binding the lipolysis stimulated lipoprotein receptor (LSR). Proteolytic cleavage promotes CdtB oligomerization into a prepore which allows for CdtA binding. Conversion to a pore and acidification within the endosome allows for translocation of CdtA into the cytosol. This talk will describe recent progress in elucidating structures of CdtB and CdtA-CdtB complexes along with the emerging understanding of TcdA/TcdB pore formation.