Myeloproliferative disorders (MPDs) constitute a group of hematopoietic malignancies that feature enhanced proliferation and survival of one or more myeloid lineage cells. William Dameshek is credited for introducing the term "MPDs" in 1951 when he used it to group chronic myeloid leukemia (CML), polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF) under one clinicopathologic category. Since then, other myeloid neoplasms have been added to the MPD member list: chronic neutrophilic (CNL), eosinophilic (CEL) and myelomonocytic (CMML) leukemias; juvenile myelomonocytic leukemia (JMML); hypereosinophilic syndrome (HES); systemic mastocytosis (SM); and others. Collectively, MPDs are stem cell-derived clonal proliferative diseases whose shared and diverse phenotypic characteristics can be attributed to dysregulated signal transduction--a consequence of acquired somatic mutations. The most recognized among the latter is BCR-ABL, the disease-causing mutation in CML. Other mutations of putative pathogenetic relevance in MPDs include: JAK2V617F in PV, ET, and PMF; JAK2 exon 12 mutations in PV; MPLW515L/K in PMF and ET; KITD816V in SM; FIP1L1-PDGFRA in CEL-SM; rearrangements of PDGFRB in CEL-CMML and FGFR1 in stem cell leukemia-lymphoma syndrome; and RAS/PTPN11/NF1 mutations in JMML. This increasing repertoire of mutant molecules has streamlined translational research and molecularly targeted drug development in MPDs.