This chapter presents a state of the art summary of pancreatic endocrine tumors (PET) in relation to its biology, epidemiology, disease mechanisms, clinical signs, diagnosis, treatment and prognosis. Tumors affecting the endocrine pancreas include glucagonoma, insulinoma, somatostatinoma, gastrinoma, vasoactive intestinal peptide secreting, growth hormone releasing factor secreting, adrenocorticotropin hormone secreting, PET causing carcinoid syndrome, PET causing hypercalcemia, and nonfunctioning PET, which together account for 5% of pancreatic tumors. PET accounts for 5% of all pancreatic neoplasms and has an annual incidence of one to five cases per million clinically and a rate of 0.5%–1.5% in autopsy studies. Diagnosis for PET involves endocrine testing, imaging, and histology in order to fully assess the tumor grade, identify the primary and metastatic loci, and determine the functionality of the tumor. PET usually is a solitary, soft, tan-yellow, well-demarcated mass with a fibrous capsule and necrosis/degeneration.