Dietary behavior seems to be an important modifiable determinant for the risk of cancer. The evidences from several epidemiological studies suggest that higher intakes of fruits and vegetables have been associated with lower risk of cancer. Dietary phenolic and polyphenolic substances, terpenoids, dietary fibers, fish oils, some micronutrients present in foods of both plant and animal origin, and a reduction of caloric intake appear to inhibit the process of cancer development. Many dietary factors possess antioxidant and anti-inflammatory properties and cause induction of phase II enzymes like glutathione-S-transferases. It has been suggested that cruciferous vegetables play an important role in cancer prevention, and their chemopreventive effects are due to high glucosinolate content which under enzymatic hydrolysis produces bioactive compound isothiocyanates. Further, isothiocyanates of a wide variety of cruciferous vegetables are powerful inhibitors of carcinogenesis in experimental animal models. Several flavonoids present in fruits, tea, soya beans, etc. may be useful as cancer preventive agents. Similarly, ellagic acid, perillyl alcohol and resveratrol found in various fruits may have chemoprotective effect. Moreover, different vanilloids such as curcumin and gingerol have been shown to possess antioxidative properties. Nevertheless, in spite of several studies, still the effects of various ingredients are not clearly distinguished. In human, little convincing evidence has been established for the proposed protective effects of dietary constituents. It is an important future research goal to provide necessary evidences to support the chemopreventive role of different dietary factors, and also to clarify misunderstandings in this perplexing area.