Withania somnifera Dunal, commonly known as ashwagandha, has been used for centuries in Ayurvedic medicine to increase longevity and vitality. Western research supports its polypharmaceutical use, confirming antioxidant, anti-inflammatory, immune-modulating, and antistress properties in the whole plant extract and several separate constituents. This article reviews the literature pertaining to Withania somnifera and its botanical constituents as antitumor agents and in conjunction with radiation and chemotherapy treatment. Following a search of MEDLINE and EBSCO databases, it can be concluded that Withania somnifera reduces tumor cell proliferation while increasing overall animal survival time. Furthermore, it has been shown to enhance the effectiveness of radiation therapy while potentially mitigating undesirable side effects. Withania somnifera also reduces the side effects of chemotherapeutic agents cyclophosphamide and paclitaxel without interfering with the tumor-reducing actions of the drugs. These effects have been demonstrated in vitro on human cancer cell lines, and in vivo on animal subjects, but there have been no human trials to date. Given its broad spectrum of cytotoxic and tumor-sensitizing actions, Withania somnifera presents itself as a novel complementary therapy for integrative oncology care.