Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are constantly produced in all aerobic organisms, mostly as a consequence of normal cellular aerobic respiration. Many factors outside the body, such as unhealthy diets and behaviors, exposure to environmental pollutants and radiation pollution, also trigger the production of abnormally high concentrations of highly reactive and toxic ROS and NOS in tissues and organs of biological systems. The excessive production of ROS/RNS causes damage to DNA, proteins and lipids and can increase the risk of cancer. Antioxidants maintain redox homeostasis and prevent ROS-/RNS-induced damages that have been associated with cancer development. In the body, antioxidant defense systems include endogenous (enzymatic and non-enzymatic antioxidants) and exogenous antioxidants supplied by plant foods. Plants or parts of plants with medicinal properties are traditionally used in health care and disease prevention and treatment. Plants are considered relatively safe, efficient and inexpensive ways of producing several valuable molecules, including many anticancer drugs. Rational food selection based on therapeutic properties and antioxidant constituents might be a useful strategy for cancer prevention. This chapter summarises recent progress on the production and health benefits of antioxidants derived from food and medicinal plants and their use in cancer prevention and treatment. This chapter also outlines the most recent anti-cancer drugs originally derived from medicinal plants and discusses lead structures isolated from a natural product with anticancer potential use as adjuvants in conventional anticancer drugs.