This volume deals with all the known aspects of somatostatin, one of the phylogenetically oldest hormones, which is a regulatory peptide with remarkable characteristics. It is a non-classical neurotransmitter discovered less than 20 years ago in both the central nervous system and in the gastroenteropancreatic system, regulating the secretion of both pituitary and digestive hormones. It also ensures nutrient homeostasis and has therapeutic uses.