Free radicals as by-products are produced from oxidation processes occurring continuously in living cells in the body. These free radicals are source of causing damage to human body. Antioxidants are organic compounds which are present as nutrients in food. One of their roles is to scavenge free radicals and thus slow down damaging processes in our body. The text covers detailed investigations and comprehensive description of antioxidants in quenching environmental toxicants as well as biological free radicals by using cyclic voltammetry and spin trapping ESR techniques. By these techniques types of interactions, extent of antioxidants to interact with free radicals in model lipid system, diffusion coefficients, rate constants, antioxidant activities and possible reaction mechanistic paths were determined. These studies give an insight to understand mechanism of antioxidant action and to determine the relative effectiveness of antioxidants as free radical quencher and would further help to explore new and more effective antioxidants for medicinal, pharmaceutical, cosmetics and food industries.