Essential thrombocythemia (ET) and polycythemia vera (PV) are myeloproliferative neoplasms (MPN), wherein JAK2 V617F mutation exists as a common driver mutation, and the JAK-STAT pathway is constitutively activated. The treatment goal for ET and PV is the prevention of thrombosis and bleeding. The treatment strategy for ET is careful observation or antiplatelet therapy with or without cytoreductive therapy based on the thrombotic risk. The treatment strategy for all PV patients is phlebotomy with a target hematocrit of <45% in addition to antiplatelet therapy. Moreover, for patients at a high risk of thrombosis, additional cytoreductive therapy is considered beneficial. In this session, we discuss important points for ET diagnosis, thrombotic risk stratification, and the details of treatment strategy and current practice with evidence from clinical trials in ET. Furthermore, current topics in the treatment of ET and PV will be introduced with a focus on clinical data about interferon-α, which is reported to induce not only hematologic response but also molecular and histopathologic response in MPN.