to the Second Edition RESEARCH INTO MEMBRANE-ASSOCIATED PHENOMENA HAS EXPANDED VERY greatly in the five years that have elapsed since the first edition of Biological Membranes was published. It is to take account of rapid advances in the field that we have written the present edition. There is now general acceptance of the fluid mosaic model of membrane structure and of the chemiosmotic interpretation of energetic processes, and our attention has shifted from justifying these ideas to explaining membrane functions in their terms. Much more information has become available concerning the role of the plasma membrane in the cell's recognition of and response to external signals, and this is reflected in the increased coverage of these topics in the book. The general form of the book remains the same. As before, a list of suggested reading, sub-divided by chapter, is provided and this has been expanded to include a greater proportion of original papers. The book is still primarily designedas an advanced undergraduate text and also to serve as an introduction for post-graduate workers entering the field of membrane research. We have taken cognizance of the comments of many reviewers, colleagues and students on the first edition and thank them for their contributions. In particular we wish to acknowledge our colleagues R. Eisenthal, G. D. Holman, D. W. Hough, and A. H. Rose. Dr. C. R.