Multiple myeloma, a B cell malignancy of the plasma cells, remains incurable. Advances in high-dose chemotherapy and stem cell transplantation have improved overall survival and event-free disease periods, but relapses are inevitable. New therapeutic agents have shown promising clinical use in patients with relapsed or refractory multiple myeloma. This article discusses the therapeutic applications of these novel agents with a focus on immunomodulatory drugs, proteasome inhibitors, and arsenic compounds.