This book was originated from a series of lectures given in a course on the physical properties of biological membranes and their functional implica­ tions. The course was intended to allow students to get acquainted with the physical techniques used to study biological membranes. The experience was valuable and we feel that a detailed description of the procedures used and of various examples of the results obtained allowed many students to become familiar with a theme that is not often part of regular courses on membrane physiology or biophysics. This book is designed as a tutorial guide for graduate students interested in understanding how physical methods can be utilized to study the proper­ ties of biological membranes. It includes first a detailed description of applications of physical techniques-such as X-ray fiber diffraction methods (Chapter 1), 2H and 13C NMR spectroscopy (Chapter 2), and calorimetry (Chapter 3)-in the study of the properties of lipid model membranes. A description of how to measure molecular mobility in membranes (Chapter 4) follows, and the book concludes with three chapters in which biological membranes are the subject of study. Chapter 5 deals with the acetylcholine receptor and its membrane environment; Chapter 6 discusses how fluorescence techniques can be applied in the study of the calcium ATPase of sarcoplasmic reticulum; and Chapter 7 explains how protein­ lipid interactions modulate the function of the sodium and proton pumps.