Lenalidomide (REVLIMID™), an immunomodulatory compound targeting both cancer cells and their microenvironment, has substantial activity in several difficult-to-manage hematological malignancies. In previously treated multiple myeloma, lenalidomide produces high-quality responses combined with sustained disease control. Recently, several randomized studies have demonstrated a clinical benefit of continuous lenalidomide treatment in newly diagnosed multiple myeloma. In many patients with refractory anemia associated with lower risk myelodysplastic syndromes and a 5q chromosome deletion, lenalidomide leads to transfusion independence, considerably improving quality of life. It has a manageable safety profile, and its oral formulation reduces the burden on patients. Several phase III trials are ongoing in other indications currently underserved by conventional therapy, such as chronic lymphocytic leukemia, non-Hodgkin's lymphoma, and prostate cancer. Several early-stage studies are exploring lenalidomide alone and in combination across different hematological malignancies, solid tumors, and immune-related disorders.