Myelodysplastic syndromes (MDS) are a set of oligoclonal disorders of hematopoietic stem cells characterized by ineffective hematopoiesis that manifest clinically as anemia, neutropenia, and/or thrombocytopenia of variable severity. The result often is transfusion-dependent anemia, an increased risk of infection or hemorrhage, and a potential to progress to acute myelogenous leukemia (AML). Although progression to acute leukemia can lead to death in patients with MDS, many deaths are consequences of cytopenias and marrow failure in the absence of transformation. Approximately 2/3 of patients succumb to the disease within 3-4 years after presentation, and individuals with high-risk MDS generally survive about 1 year. Given that the disease is more prevalent in the elderly who often have comorbid conditions, the current treatment of MDS consists mainly of supportive care. Curative treatments are restricted to younger, healthy individuals with histocompatible (HLA)-matched donors for allogenic transplant or those able to undergo intensive chemotherapeutic regimens. However, understanding of the pathophysiology of MDS and identification of potential cellular and molecular targets in recent years has led to novel therapeutic approaches. Encouraging results using these heterogeneous therapeutic approaches alone or in combination in Phase I and II trials, have, in turn, called into question previous classification systems and have confirmed the need for an all-encompassing molecular, diagnostic and prognostic staging system.