During the embryonic development of the eye, a group of founder cells in the optic vesicle gives rise to multipotent progenitor cells that generate all the neurons and the Müller glia of the mature retina. In most vertebrates, a small group of retinal stem cells persists at the margin of the retina, near the junction with the ciliary epithelium. In fish and amphibians, the retinal stem cells continue to produce progenitors throughout life, adding new retina to the periphery of the existing retina as the eye grows. In birds the new retinal addition is more limited, and it is absent in those mammals that have been analyzed. Nevertheless, cells from the retinal periphery and ciliary body of mammals can be isolated and grown in vitro for extended periods. Methods for the study of both embryonic progenitors and adult retinal stem cells in vitro and in vivo have led to a better understanding of retinal development, allowed for the screening of factors important in retinal growth and differentiation, and enabled the development of methods to direct stem and progenitor cells to specific fates. These methods may ultimately lead to the development of strategies for retinal repair.