Although the use of oxygen as metabolic fuel allows an attractive harvest of energy rich phosphates per molecule of glucose, a significant fraction of oxygen utilized by the body incompletely reduced and is known to be toxic. Such partially reduced forms of oxygen and some of their derivatives are highly reactive pro-oxidants that are collectively referred to as reactive oxygen species (ROS). A multitude of factors are known to modulate the amount of ROS formation in the body. To escape ROS dependent toxicity biological structures have their protective machinery in the form of physiological antioxidants. It appears that the physiological antioxidants are not independently capable of completely detoxifying the ROS constantly produced by the body. The supply of exogenous antioxidants is thus crucial. Endo- and exogenous antioxidants act in concert to minimize ROS dependent damage. ROS are involved in the pathogenesis of a large number of clinical disorders. The sensitive balance between the pro- and anti- oxidant forces in the body appears to be very crucial in determining the state of health, well being and longevity. This article presents an introductory overview covering the current concepts related to oxidants and antioxidants with special reference to human health.