Over the past decade, the advances in our understanding of stem cell biology and the role of stem cells in diseases, such as colorectal cancer, have been remarkable. In particular, discoveries related to the control of stem cell proliferation and how dysregulation of proliferation leads to oncogenesis have been foremost. For intestinal stem cells, the WNT family of growth factors, and events such as the regulation of the nuclear localization of beta-catenin, seem to be central to normal homeostasis, and mutations in the components of these pathways seem to lead to the development of colorectal cancer. A paradigm of abnormal stem cell biology is illustrated by patients with familial adenomatous polyposis, who have mutations in the adenomatous polyposis coli gene. The wild-type protein encoded by this gene is important for the prevention of mass beta-catenin accumulation in the nucleus and the subsequent overtranscription of cell cycle proteins. This review discusses the basic mechanisms behind stem cell regulation in the gut and follows their role in the natural history of tumor progression.