The cornea on the front surface of the eye provides our window to the world. Maintenance of corneal transparency is dependent on the integrity and functionality of the outermost corneal epithelium which itself is maintained throughout life by a population of limbal epithelial stem cells (LESC). If this adult stem cell population is depleted by injury or disease, the transparency of the cornea and therefore vision is threatened. LESC deficiency results in corneal opacification, inflammation, vascularization, and severe discomfort. Cultured LESC therapy is one of only several examples of the successful use of an adult stem cell therapy in patients. Hence, the ready accessibility of a transparent stem cell niche and the clinical precedence for use of stem cell therapy make the cornea a unique and excellent model for the study of adult stem cells in health and disease. This review will discuss our current understanding of LESC biology, pathology, and therapeutic application.