The adult intestinal epithelium contains a relatively simple, highly organized, and readily accessible stem cell system. Excellent methods exist for the isolation of intestinal epithelium from adults, and as a result collecting large quantities of intestinal stem and progenitor cells for study or culture and subsequent clinical applications should be routine. It is not, however, for two reasons: (1) adult intestinal epithelial cells rapidly initiate apoptosis on detachment from the basement membrane, and (2) in vitro conditions necessary for survival, proliferation, and differentiation are poorly understood. Thus to date the study of intestinal stem and progenitor cells has been largely dependent on in vivo approaches. We discuss existing in vivo assays for stem and progenitor cell behavior as well as current methods for isolating and culturing the intestinal epithelium.