Well over one decade has passed since the appearance of the original four volumes of Membrane Transport in Biology. Since the publication of the last volume there have been spectacular advances in this field. These advances have been in part the result of the application of exciting new methodologies, and in part the result of new insights into the regulation and integration of transport processes. This volume, as well as a sixth volume, which is in preparation, are intended to cover key areas in which the development has been particularly striking. For many years the trend in studies of membrane transport had been that of increasing specialization with regard to the transporter of interest and of the cell or tissue studied. This trend was supported by the enormous number of publications directed at understanding the cellular physiology of specific organ systems and tissues, and also by the fact that different tissues often seemed to react so differently to the same conditions that mechanisms unique to each appear to be at play. One of the happy developments in recent years has been the realization that this apparent disparity of behaviors in different tissues is based on varying combinations of a limited number of transport mechanisms, all mediated by the same or similar proteins. Some of these transport proteins have already been isolated and analyzed with respect to amino acid sequence whereas others are just entering this phase.
