Pancreatic neuroendocrine neoplasms(pNEN) have neuroendocrine differentiation with expression of synaptophysin or chromogranin A and was called as “islet cell tumor” in the past and have been called as “carcinoid tumor” in other organs except pancreas. Depending on the presence of paraneoplastic symptom induced by abnormal hormone or bioamines produced by tumor cells, pNEN can be called as “insulinoma”, “glucagonoma”, “somatostatinoma”, or “gastrinoma”, etc. Generally, pNENs slowly grow, but some patients have poor prognosis after distant metastasis. Historically classification of pMENs has been focused on the prediction of prognosis and prognostic factors such as functioning of tumor cells, angioinvasion, or presence of metastasis were used as criteria of classification. Since 2010, pNEN has been graded into G1, G2, and G3 based on the proliferative index of tumor cells and staging system of exocrine pancreatic neoplasm has been applied to pMEN. Based on the clinicopathologic and molecular studies, new classification of pMEN was launched in 2017. In the new classification, the degree of differentiation of tumor cells as well as the proliferative capacity is an important classification criterion, because well differentiated pNEN and poorly differentiated pNEN have different biological and clinical features. This time, new classification and staging system of pMEN will be introduced with the evidence and detailed rules in diagnostic practice.