The biological tissues from which foods originate contain multicomponent antioxidant systems that include free radical scavengers, metal chelators, singlet oxygen quenchers, and antioxidant enzymes. Our understanding of how these endogenous antioxidants protect foods from oxidation is still in its infancy. In addition, how factors that can alter the activity of endogenous food antioxidants (e.g., heat processing, irradiation, and genetic selection of foods high in antioxidants) is still poorly understood. Finally, research is continuing to show that natural food antioxidants in the diet are very important in the modulation of disease. Thus, finding mechanisms to increase natural food antioxidants may be beneficial to both health and food quality.