In this ground–breaking practical reference, the family of aspartic acid proteases is described from a drug developer′s perspective. The first part provides a general introduction to the family of aspartic acid proteases, their physiological functions, molecular structure and inhibition. Parts two to five present various case studies of successful protease inhibitor drug design and development, as well as current and potential uses of such inhibitors in pharmaceutical medicine, covering the major therapeutic targets HIV–1 protease, renin, beta–secretase, gamma–secretase,plasmepsins and fungal proteases.