Bortezomib (Velcade, Millennium) is the first proteasome inhibitor to be used in clinical practice and is indicated for the treatment of multiple myeloma patients who have received at least one prior therapy. Bortezomib inhibits the intracellular degradation of proteins necessary for normal cell cycling and function. This, in turn, results in cell-cycle arrest and apoptosis. Bortezomib has shown significant activity in trials of patients with relapsed or refractory multiple myeloma; approximately one third of patients have shown significant improvement with bortezomib monotherapy in phase II and III clinical trials. Early phase trials are also evaluating bortezomib in combination with other agents used in the treatment of multiple myeloma, including melphalan, prednisone, thalidomide, and lenalidomide. Preliminary data suggest that bortezomib may act synergistically with some agents, and improves response rates. Bortezomib is generally well tolerated, but common side effects include peripheral neuropathy and thrombocytopenia. Studies are underway to explore different dosing strategies as well as ways to maximize patient benefit while reducing toxicity. This review will discuss what is known thus far about the efficacy and safety profile of bortezomib, ways for optimizing treatment with bortezomib, and strategies for managing side effects and enhancing quality of life.