The cancer-preventive activities of tea and some tea constituents, such as caffeine and (-)-epigallocatechin-3-gallate (EGCG), have been demonstrated in animal models. The mechanisms of action of the tea constituents have been extensively investigated, but the mechanisms for the cancer-preventive activity of tea are not clearly understood. This chapter discusses some of the reported studies on the green tea polyphenol, EGCG, and the major issues in the interpretation of these data. Among the different activities of EGCG observed in cell culture systems, we need to select the physiologically relevant ones based on the biological importance of the target as well as the effective concentration and whether the reaction can take place in vivo because of the limited bioavailability of EGCG. We also need to distinguish between primary and subsequent events. Possible artifacts should be recognized. The cancer-preventive mechanisms need to be validated in animal models or human samples.