Biological membranes have been under intensive investigation for several decades. Despite very great experimental challenges, membranes are at last beginning to reveal their secrets. In this book, leading investigators of membrane structure and function report on progress in three related fields: specialization of membrane regions, asymmetry in transport properties, and differentiation of cell faces in epithelia. "Specialization at the Molecular Level" is the subject of the first section; in it, the authors consider such problems as the biogenesis of membranes, the geometry of protein-lipid relationships, and the physical properties of membrane receptor-sites. In the second section, "Asymmetry in Transport," such topics as the sodium-potassium pump, proton translocation, and anion transport are covered. The last section is entitled "Polar Faces in Epithelia" and deals with the complex properties of ion transport across the complex membrane environment maintained by surfaces such as the renal tubular epithelia.