Free radicals are produced as part of normal cellular function. They may also be produced by endogenous and environmental sources. The human body has several mechanisms to counteract oxidative stress by producing antioxidants, which are either naturally produced in situ, or externally supplied through foods and/or supplements. Antioxidants prevent free radical induced tissue damage by preventing the formation of radicals, scavenging them, or by promoting their decomposition. This paper reviews the mechanisms of formation and catabolism of the free radicals and also discusses with potential role of the antioxidants in preventing and repairing damages caused by oxidative stress.