Developmental biology is one of the most exciting and fast-growing fields today. In part, this is so because the subject matter deals with the innately fascinating biological events¿changes in form, structure, and function of the organism. The other reason for much of the excitement in developmental biology is that the field has truly become the unifying melting pot of biology, and provides a framework that integrates anatomy, physiology, genetics, biochemistry, and cellular and molecular biology, as well as evolutionary biology. No longer is the study of embryonic development merely ¿embryology.¿ In fact, development biology has produced important paradigms for both basic and clinical biomedical sciences. Though modern developmental biology has its roots in ¿experimental embry- ogy¿ and the even more classical ¿chemical embryology,¿ the recent explosive and remarkable advances in developmental biology are critically linked to the advent of the ¿cellular and molecular biology revolution.¿ The impressive arsenal of expe- mental and analytical tools derived from cell and molecular biology, which promise to continue to expand, together with the exponentially developing sophistication in fu- tional imaging and information technologies, guarantee that the study of the devel- ing embryo will contribute one of the most captivating areas of biological research in the next millennium.