Pancreatic beta cells are responsible for maintaining the body's glucose levels within a very narrow range; their population is dynamic, with compensatory changes to maintain euglycemia. Throughout the lifetime of a mammal, low levels of beta-cell replication and apoptosis are balanced and result in a slowly increasing mass of beta cells. The emphasis in this review is on recent insights on the natural history of the beta cell in a normal pancreas: sources of renewal, survival and changes in differentiation.