The main purpose of this book is to unify approaches and ideas in the field of aneural sensory transduction. This field has recently come to the attention of several research groups in various disciplines, and their number seems to be growing. Unfortunately, because of the diverse scientific backgrounds of the researchers in the field, the apparent heterogeneity of experimental techniques (i. e. , behavioral response analysis, sophisticated biochemical and genetic manipulations, conventional and pulsed laser spectroscopy) and theoretical approaches may be discouraging, for both the experienced worker and the new- comer. Actually, this heterogeneity is more apparent than real, and unifying concepts, approaches, and ideas already exist, particularly with respect to all the questions concerning the role of membranes and their properties (such as ion permeability, electric potentials, and active transport) in the various steps of sensory perception and transduction processes. It is currently accepted that most, if not all, the fundamental facts in molecular sensory physiology of aneural organisms, be they chemosensory, photosensory, or geosensory, can ultimately be understood in terms of a few basic ideas. Each chapter of this book emphasizes and clarifies the role of mem- brane properties and phenomena in the particular sensory response examined. Of course, in some cases, this task has been rather complex because of the limited amount of experimental data clearly supporting a membrane-based model of sensory transduction.