Representative diseases of BCR/ABL-negative myeloproliferative neoplasms (MPN) are polycythemia vera (PV), essential thrombocytosis (ET), and primary myelofibrosis (PMF). It was reported in 2005 that there is a common genetic mutation in Exon 14 of the JAK2 gene in MPN cases. The gene mutation is a point mutation at which the 617th amino acid of the JAK2 protein is substituted from valine to phenylalanine and is referred to as the JAK2 V617F mutation. Subsequently, JAK2 Exon 12 mutation, MPL gene mutation, and CALR gene mutation were detected in 2013, and it was revealed that in almost all cases of BCR/ABL- negative MPN, any gene mutation could be involved as a driver gene mutation. As a result, in the WHO classification 2016, gene mutation analyses of JAK2, MPL, and CALR were incorporated into the diagnostic criteria. Analysis of gene mutation is indispensable for the diagnosis of MPN. Also, its importance as an inspection item is increasing. [Review].