In 1813, Vautier published his observation of tumor regression in patients who had suffered from gas gangrene. Since then, many publications have described the use of bacteria as antitumor therapy. For example, Bifidobacterium and Clostridium have been shown to selectively colonize tumors and to reduce tumor size. In addition, recent studies have focused on the use of genetic engineering to induce the expression of pro-drug converting enzymes, cytokines, specific antibodies, or suicide genes in tumor-colonizing bacteria. Moreover, some animal experiments have reported the treatment of tumors with engineered bacteria, and few side effects were observed. Therefore, based on these advances in tumor targeting therapy, bacteria may represent the next generation of cancer therapy.