The intestinal epithelium is one of the fastest renewing tissues in mammals and plays a critical role in food digestion and nutrient absorption, maintenance of mucosal barrier, immune regulation, and defense against intestinal microbiota. The diverse cell types within the intestinal epithelium provide the foundation for its multifunctional roles, and their differentiation and development are tightly controlled. Dysregulation of key regulatory signals can compromise the intestinal epithelial barrier function and contribute to the occurrence of various intestinal diseases. This review discusses the functions, cellular composition, and regulatory signals of the intestinal epithelium.