Glucagon-like peptide-1 (GLP-1) is an incretin, boosting prostprandial insulin secretion, and anorexic hormone released from so called L-cells found scattered in the intestinal epithelium. GLP-1 mimetics and inhibitors of dipeptidy-peptidase-4, which prolong the plasma half-life of incretins are now widely used in the treatment of diabetes. An alternative strategy is the recruitment of endogenous GLP-1 “reserves”, as L-cells increase in number in the distal intestine and increased GLP-1 secretion has been correlated with improved glucose homeostasis after gastric bypass surgery. We used transgenic mouse models to identify and study L-cells and GLP-1 receptor expressing target cells. Interestingly, proximal and distal L-cells differ in their expression profiles, with duodenal/jejunal L-cells co-expressing glucose-dependent insulinotropic polypeptide and cholecystokinin, while colonic L-cells co-express the anorexigenic peptide peptideYY and, with increasing frequency towards the rectum, orexigenic insulin-like peptide-5. Intestinal L-cells are open-type enteroendocrine cells with apical microvilli making direct contact with luminal contents. While duodenal/jejunal L-cells are likely to be exposed to primary nutrients such as glucose, dipeptides/amino acids and long-chain free fatty acids, more distally located colonic L-cells would more likely encounter bacterial fermentation products, such as short chain fatty acids and indole, a breakdown-product of tryptophan. We found the response of L-cells to glucose and dipeptides to involve electrogenic sodium/proton coupled nutrient uptake, resulting in increased action potential frequency and elevation of cytosolic calcium. While indole widened action potentials through inhibition of voltage-gated potassium channels, it also reduced cytosolic ATP levels, thereby inhibiting GLP-1 secretion over longer exposure times. Short-chain fatty acids recruited the Gq-coupled receptor FFAR2, leading to acute stimulation of GLP-1 secretion from colonic cultures. Other luminal factors, such as allyl isothiocyanate, the pungent component of mustard, and bile acids can stimulate L-cells through activation of the TrpA1 cation channel and the predominantly Gs coupled receptor GPBAR-1, respectively; while it was thought that GPBAR1 directly monitors luminal bile acids I will present evidence for a basolateral location of GPBAR-1. Characterising the pathways and receptors underlying L-cell stimulation is hoped to identify new therapeutic opportunities for the treatment of diabetes and obesity.