Formerly named carcinoids, neuroendocrine tumors originate from diffuse endocrine cells, can involve any part of the gastrointestinal tract, endocrine pancreas and bronchopulmonary (BP) tree, and have a wide range of malignant potential. This chapter summarizes the data available on the epidemiology of neuroendocrine neoplasia (NEN) from around the world, including the relative frequency according to organ of origin, annual incidence rates (IR) and trends in IR at the various anatomic sites, age and stage at presentation, racial and gender differences in IR and 5-year survival rates. Over time, changes have been made in the classification and registration of NEN, both in the same registry and across the globe, thus confounding the possibility to draw conclusions as to the true rise in IR of NEN that is observed all over the world. BP NEN has become the most common site in many western countries, while NEN of the rectum is more common in the Far East. In some countries, appendiceal NEN is the most common site in females. When compared to adenocarcinoma of the same location, the prognosis of NEN patients is better. Five-year survival rates are highest for NEN originating in the rectum and appendix, but lower in small intestinal and pancreatic NEN. Future research is needed to understand the contribution of genetic and environmental factors to NEN epidemiology.