The study of cellular receptors is one of the fundamental issues in membrane biology. These vitally important membrane proteins have only recently become the subject of intensive investigation; however, a wealth of experimental data has already been accumulated within a relatively short period. Research on cellular receptors is essential for understanding the functions of biological membranes and, more broadly, the principles of cell biology as a whole. This book provides, for the first time, a systematic exposition of the fundamental knowledge concerning cellular receptors, including their structural organization, the characteristics of functionally important domains, the molecular genetics of cellular receptors, as well as their biosynthesis and catabolism. Particular attention is devoted to the functional roles of cellular receptors in regulating biochemical processes, including the transport of metabolites into cells, cell proliferation, gene expression, and the regulation of protein biosynthesis through feedback mechanisms. These topics have become integral components of biochemistry and biophysics curricula in university and medical-school departments of medical biology, or are taught as part of an independent course entitled Membrane Biochemistry. The field of cellular receptor research encompasses an exceptionally broad range of issues, touching upon virtually every major aspect of cell and molecular biology. Many questions within this field remain insufficiently studied, while some established concepts can hardly be regarded as definitive conclusions. The rapid accumulation of experimental data makes it difficult to arrive at final judgments, yet at the same time creates opportunities for the development of new hypotheses. The author believes that the most promising of these hypotheses are reflected in this book. Their critical analysis will enable readers to develop their own informed perspectives on this important area of membrane-process biochemistry.