The digestive system represents the most common localization for neuroendocrine neoplasms (NEN) in the human body. Despite a common classification and some unifying characteristics, for example the tissue and serum markers used for their identification and characterization and their features at imaging, NEN of the digestive system display a high level of morphological, molecular, clinical, and biological heterogeneity. This is partially related to distinct causative factors and pathogenetic mechanisms, which are peculiar to the specific localizations in the digestive system. This chapter presents a comprehensive overview of NEN of the digestive system with focus on their epidemiology, histopathology, molecular biology, imaging characteristics, and therapeutic options. Subchapters deal with the problematic of differential diagnosis and treatment of hepatic metastases of NEN, which frequently represent a clinical challenge, and with NEN occurring in the context of genetic syndromes.[Aspects of disease that affect the small bowel are also covered in Chapter Unavailable ].