Intercellular adhesive events are involved in a wide range of biological processes, including pattern formation and morphogenesis during development, immune responses, leukocyte recirculation, wound repair, tumour growth and metastasis. In the multicellular state, signals from cell adhesion molecules, along with those from growth factor and cytokine receptors, provide a range of information to the cell that is integrated to yield a final message, perhaps to maintain the cell cycle (if it is a stem cell) or follow a path towards terminal differentiation. Aberrant cell adhesion plays a key role in many developmental defects, acute and chronic inflammatory disease and cancer.