The organs of the vertebrate digestive system arise from an endodermally-derived tube called the primitive gut, which is surrounded by splanchic mesoderm. During embryonic patterning, intercellular signaling from mesodermal cells is thought to influence the specification of endodermal epithelial cells in the gut tube. For instance, Wnt signaling regulates liver specification. Intercellular signaling also induces the compartmentalization of the primitive gut into three regions along the anteroposterior axis: foregut, midgut, and hindgut. Within each region, cell specification, differentiation, and tissue morphogenesis establish the major digestive system organs. The foregut derivatives include esophagus, stomach, liver, and pancreas. Signaling within the midgut gives rise to the jejunum, ileum, and ascending colon. The hindgut derivatives include the descending colon and rectum. Postnatally, epithelial stem cell proliferation and differentiation are important for maintaining the intestinal compartment. In addition, recent evidence indicates that progenitor cells in the liver and pancreas influence tissue homeostasis in adults.