A review of progress in a field as broad as cell motility will be a selection of topics that reflects the interest of the reviewer. I will restrict the subject even further by concentrating on a single problem, the progress in our understanding of the physicalchemical basis of motility. One measure of progress in cell biology is the extent to which the description of a phenomenon is replaced by a chemical mechanism. An understanding of the mechanisms of individual processes studied in isolation still comes far short of a science of cell biology, which must deal with the integration of processes into a description of the cell as a functional unit. Considerable progress has been made in the understanding of individual processes but their integration in the cell remains a problem to be studied over the next 20 years.
Studies on a wide variety of cells and tissues have led...
