A brief history of leather as a bookbinding material is combined with an explanation of the chemistry of leather and its environmental needs. Goals for library leather-bound volumes are: 45-55% R.H., 75°F., no light (or filtered light), and cleaning and treating of the leather. Formulas: the buffering salt solution -- potassium lactate 7%, paranitrophenol 0.25%, distilled water 92.75%; lubricant dressing -- neat's-foot oil 60%, lanolin (anhydrous) 40%. Third in Library of Congress Preservation Leaflet Series.