Since 2005 driver mutations have been identified in more than 90% of patients with myeloproliferative neoplasms, providing substantial insight into their pathogenesis and leading to the development of JAK inhibitor drugs. Ruxolitinib, the first one available, has shown activity whatever the presence of Janus Kinase 2 mutation, in reducing splenomegaly, improving cytopenias, alleviating constitutional symptoms and finally improving survival (COMFORT I and II studies). In France, access to ruxolitinib has been possible since April 2011, before wider availability in November 2012.