Cell surface membranes contain a range of types of molecule of which proteins form a significant part, and which play important roles in regulating cellular activities, such as growth and differentiation. In recent years considerable advances have been made in the understanding of the structure and function of cell surface molecules, partly stimulated by the development of recombinant DNA technologies. This book provides a review of current knowledge of the molecular biology of the cell surface with particular emphasis on cell differentiation, relating the molecular properties of the cell surface to developmental biology. In addition to the central theme of cell differentiation, cell surface markers, which are useful in monitoring differentiation and cell adhesion molecules, which influence differentiation, are covered.