The study of the structure and function of bovine pancreatic carboxypeptidase A has a long historical record which began in 1937 with the isolation of the crystalline enzyme by Anson (1937). Although the literature of this exopeptidase has been reviewed on several occasions (Neurath & Schwert 1950; Smith 1951; Neurath 1960; Vallee 1964; Neurath, Bradshaw, Ericsson, Babin, Petra & Walsh 1968; Vallee & Riordan 1968; Lipscomb, Hartsuck, Reeke, Quiocho, Ludwig, Steitz & Bethge 1968), nevertheless, it seems appropriate at the outset of a conference on carboxypeptidase to review in brief the major contributions that have been made over the years to the study of the structure and function of this enzyme, as summarized in table 1.