Craniofacial morphogenesis is a complex process and the blueprint for building the vertebrate head and face is established very early during embryonic development. In fact in humans, the most critical steps take place between about the third to eighth weeks of pregnancy. The facial region of the embryo starts out as a relatively blank slate, consisting of three distinct tissue layers known as ectoderm (outside), mesoderm (middle), and endoderm (inside) lying adjacent to one another. Shortly thereafter, the most critical step of head and facial development occurs; the formation of neural crest cells. Neural crest cells are derived from the neural ectoderm and migrate over long distances ultimately forming cartilage, bone, connective tissue, sensory neurons, glia, and pigments cells amongst many other cell types and tissues. Neural crest cells therefore generate the scaffold upon which the head and face are constructed and are largely responsible for facial shape and variation. The muscles of the face such as those required for jaw opening and closing (ie, mastication) are generated from the mesoderm as are the endothelial cells that form the majority of the vasculature. The lining of the oral cavity of the mouth (the beginning of the gastro-intestinal tract), the esophagus, and organs in the neck such as the thyroid and parathyroids are derivatives of the endoderm. Differential cell proliferation, cell death, cell migration, and cell differentiation occurs in each of these layers ultimately shaping and