This review will discuss some of the antioxidant assays and biomarkers/measurements used to assess the effect of dietary components on ameliorating in vivo oxidative stress. Although the development of dietary antioxidants has become a major component of the dietary supplement market, this review will focus on foods (primarily fruits and vegetables) and their impact on biomarkers of oxidative stress and the ultimate appearance of disease states. Data is reviewed demonstrating the importance of consumption of dietary antioxidants along with meals to prevent postprandial oxidative stress. Epidemiology studies have demonstrated the relationships between dietary antioxidant intake in the form of polyphenolic type compounds and health outcomes. However, additional research is needed in order to clearly define the mechanism (s) of action of the polyphenolics and whether their effects are direct or indirect in nature.