Besides being a source of nutrients, foods, particularly plant foods, are a rich source of bioactive phytochemicals or bionutrients. Studies carried out during the past 2-3 decades have shown that these phytochemicals have an important role in preventing chronic diseases like cancer, diabetes, coronary heart disease and hyper-cholesterolaemia. The major classes of phytochemicals with disease-preventing functions are dietary fibre, antioxidants, detoxifying agents, immunity-potentiating agents and neuropharmacological agents. Each class of these functional agents consists of a wide range of chemicals with differing potency. For example, antioxidant function is exhibited by some nutrients, such as vitamin E, vitamin C and provitamin A. Other phytochemicals that have antioxidant properties are carotenoids, phenolic compounds, flavonoids and isothiocyanates. Some of these phytochemicals have more than one function. Foods rich in these chemicals and exhibiting disease-protecting potential are called functional foods. Indian habitual diets, which are based predominantly on plant foods like cereals, pulses, oils and spices, are all good sources of these classes of phytochemicals, particularly dietary fibre, vitamin E, carotenoids and phenolic compounds. There is, however, much scope for further systematic research in screening Indian foods and diets for these phytochemicals and assessing their potential in protecting against chronic diseases.