Somatostatins (SST) form a family of cyclopeptides that are mainly produced by normal endocrine, gastrointestinal, immune and neuronal cells, as well as by certain tumors. By binding to G-protein-coupled receptors on target cells, SST act as neuromodulators and neurotransmitters, as well as potent inhibitors of various secretory processes and cell proliferation. In this book, the authors discuss the synthesis, mechanisms-of-action and physiological effects of somatostatins. Topics include the effects of somatostatin in animal models of retinal disease; radiolabelled somatostatin analogues for use in molecular imaging; somatostain analogs as a treatment for congenital hyperinsulinism; somatostain and its receptors in the mammalian cochlea; diagnostic accuracy of positron emission tomography with somatostatin analogues in gastroenteropancreatic and thoracic neuroendocrine tumors.