Basic research in developmental biology has undergone nothing short of a revolution during the past decade. Tremendous growth of the subject and pool of practitioners is reflected in an ever increasing number of relevant professional journals. As a result of this literature explosion, it has become increasingly difficult to keep up with all new advances in, and to synthesize an up-to-date overview of, the field.This series from Elsevier represents an attempt to consider timely issues in developmental biology research. It provides annual reviews of selected topics, written from the perspectives of leading investigators in the field of development. Each review draws heavily from the author's own research contributions and perspective and provides a valuable summary of the subject for the reader.