Numerous scientific reviews and studies described the relationship between the increase in cellular reactive oxygen radicals and the pathogenesis of several chronic diseases, including cancer. Reactive oxygen and nitrogen species are generated from endogenous (normal physiological processes) as well as exogenous sources (xenobiotic interaction). When the antioxidant control mechanisms are overrun, the cellular redox potential shifts towards oxidative stress. As a consequence, the potential for damaging cellular nucleic acids, lipids, and proteins increases. Importantly, oxidative nuclear DNA damage has an important role in neoplasia. Cancer cells exhibit increased reactive oxygen species (ROS) generation that may promote cell proliferation. Many phytochemicals have been implicated in combating oxidative stress-induced diseases such as cancer and other chronic disorders. Many of these phytochemicals have the power to inhibit cell proliferation and also to suppress the promotion and progression of cancer. Phytochemicals like flavonoids inhibit the oxidative enzymes such as 5-lipoxygenase and 12-lipoxygenase. Terpenoids, another class of phytochemicals, suppress tumor growth by inhibiting HMG-CoA reductase activity. Also, they act at various stages of tumor development, inhibit initiation and promotion of carcinogenesis, induce tumor cell differentiation and apoptosis, and suppress tumor angiogenesis. These phytochemicals also inhibit tumor invasion via the NF-κB signaling pathway and thereby modify disease-related cellular targets in cancer. Thus, many of the phytochemicals present in various herbs act in different ways and thereby, inhibit cancer initiation, promotion and also progression.