Carotenoids are ubiquitous components of edible fruits and vegetables and represent an important group of potential chemopreventive agents. In this regard, the most extensively studied carotenoid has been b-carotene, which has provitamin A activity. However, other carotenoids, such as lycopene, do not have provitamin A activity but show a higher potential to suppress experimental carcinogenesis. Carotenoids are thought to reduce the damage caused by free radicals to cell membranes and associated receptors, modulate cell immune responses, and inhibit initiated tumor cells. This chapter gives an account of the major natural carotenoids and reviews studies on their cancer-preventive activities.