Chronic myelomonocytic leukemia (CMML) is characterized by the association of myelodysplastic features and proliferation of both granulocytic and monocytic series. This disease frequently indolent, may however demonstrate progressive course and/or transform to acute leukemia. Nosologic and diagnostic problems raised by this malignant hematological pathology, its clinical and biological presentations, and current treatments are reported in this review.