Despite significant progress in the treatment of multiple myeloma (MM) over the past decade, this disease remains incurable and almost all patients ultimately experience relapse and become refractory to treatment over time. However, the outlook for patients with relapsed MM has improved markedly with the use of the immunomodulatory drugs thalidomide and lenalidomide, and the proteasome inhibitor bortezomib. Moreover, the development of new drug classes based on preclinical rationale and the introduction of next-generation agents is likely to further expand treatment options and improve outcomes for relapsed MM.