Myeloproliferative neoplasia are clonal hematological malignancies characterized by excessive proliferation of blood cells. They group together different entities and can be classified according to the presence or absence of BCR-ABL rearrangement. We distinguish between chronic myeloid leukemia, classic BCR-ABL1-negative neoplasia including primary polycythemia; primary myelofibrosis and essential thrombocythemia; chronic neutrophilic leukemia; chronic eosinophilic leukemia (without further specification) and unclassifiable myeloproliferative neoplasia. This book is a review of what is known about myeloproliferative neoplasia and what has been learned so far.