Research on embryonic cephalic neural crest cells and paraxial mesoderm is providing new information regarding vertebrate craniofacial morphogenesis. Based on recent results, a reevaluation of the roles these embryonic populations play in the development of the head has been undertaken. The following discussion will consider the possible impact of these data on our understanding of craniofacial morphogenesis.The neural crest has attracted the interest of embryologists since before the turn of the century. This attention resulted from the apparent abilities of these ectodermally derived cells to migrate extensively within the embryo, and to give rise to a diverse and heterogeneous array of tissues, including peripheral sensory and autonomic ganglia, adrenal medullary and other secretory populations, craniofacial skeletal and connective tissues, Schwann cells and melanocytes (reviewed by