So much has been learned about the surface of cells that it can almost be counted as an organelle. The surface has been revealed as a complex assembly of proteins, highly mobile in time and space, with overlapping activities and shared structural motifs. The locations of their genes and the untangling of their functions are major challenges being tackled by laboratories worldwide. The 57th annual Cold Spring Harbor Symposium brought together over 80 leading investigators to discuss data and ideas on receptor-ligand interactions, membrane organization, signal transduction, peptide transport, cell adhesion, and the regulation of developmental processes. Studies in molecular and cell biology, embryology, neurobiology, and immunology were presented. This volume of collected papers from the Symposium, like its predecessors in this most prestigious series, provides a wide-ranging, eclectic review of a topic central to the understanding of cell structure and function