In the adult, the pancreatic beta-cell mass adapts insulin secretion to meet long-term changes in insulin demand and, in particular, in the presence of insulin resistance that is either physiological, such as pregnancy, or pathophysiological, such as obesity. The failure of beta cells to compensate for insulin resistance is a major component of impaired glucose homeostasis and overt diabetes. This defect is clearly the consequence of a decline of insulin response to glucose due to functional beta-cell deficiency. It is also the consequence of an inability of the endocrine pancreas to adapt the beta-cell mass to insulin demand (pancreas plasticity), which eventually leads to a decrease in functional beta-cell mass. This idea has resulted in considerable attention being paid to the development of new therapeutic strategies aiming to preserve and/or regenerate functional beta-cell mass. The latter is governed by a constant balance between beta-cell growth (replication from pre-existing beta cells and neogenesis from precursor cells) and beta-cell death (mainly apoptosis). Disruption of this balance may lead to rapid and marked changes in beta-cell mass. Glucagon-like peptide-1 (GLP-1), an incretin, enhances beta-cell survival (by activating beta-cell proliferation and differentiation, and inhibiting beta-cell apoptosis), thus contributing to the long-term regulation of insulin secretion by maintaining a functional beta-cell mass. The development of drugs regulating this parameter will be the major challenge of the next few years in the management of type 2 diabetes.