The intestinal epithelium is a classic example of a rapidly self-renewing tissue 
fueled by dedicated resident stem cells. These stem cells reside at the crypt 
base, generating committed progeny that mature into the various functional 
epithelial lineages while following a rapid migratory path toward the villi. Two 
models of intestinal stem cell location were proposed half a century ago and 
data have been presented in support of both models, dividing the scientific 
community. Molecular markers have been identified and validated using new 
techniques such as in vivo lineage tracing and ex vivo organoid culture. The 
intestinal stem cell niche comprises both epithelial cells, in particular the 
Paneth cell, and the stromal compartment, where cell-associated ligands and 
soluble factors regulate stem cell behavior. This review highlights the recent 
advances in identifying and characterizing the intestinal stem cells and their 
defining niche.