Understanding of the pathophysiology of atherosclerosis can provide new strategies for the prevention and treatment of patients with this common disease. Clinical, epidemiologic, and basic molecular science studies have identified oxidative stress as a factor contributing to the development and progression of atherosclerosis. Oxidative stress also participates in the pathogenesis of endothelial dysfunction and hypertension, two important factors in many patients with atherosclerosis. Further, it contributes to mechanisms of disease progression such as lipid oxidation and vascular remodeling. This article reviews the role of reactive oxygen species and oxidative stress in atherosclerosis.