Intercellular adhesion is a complex phenomenon central to the development, structure and functioning of all multicellular organisms. Adhesion is mediated by distinct families of cell-adhesion molecules (CAMs), and recent studies have identified key characteristics of CAMs that influence their function. Affinity and kinetic analyses using a novel technique based on surface plasmon resonance have shown that CAM interactions that mediate transient cell adhesion may have surprisingly low affinities and extremely fast dissociation rate constants.