The 26S proteasome is a multicatalytic enzyme responsible for degradation of a large fraction of intracellular proteins. Targeting the proteasome activity is a rational and novel strategy for cancer therapy that can lead to cell death for transformed cells. Today, bortezomib, a first-in-class proteasome inhibitor, has established clinical efficacy and an approved clinical indication for the treatment of relapsed and refractory multiple myeloma. Since bortezomib has also shown to induce chemosensitization, the drug is utilized for combination with a variety of chemotherapeutics. In this review, we provide an overview of the current state of the use of bortezomib and second generation proteasome inhibitors.