After water, tea is the most widely consumed beverage. The major active constituents in green tea are catechins, of which epigallocatechin-3-gallate (EGCG) is the most abundant and active compound. Animal experimental studies using EGCG alone or green tea catechins with EGCG being a major component have generated a mounting body of evidence suggesting that EGCG as a naturally occurring compound and commonly consumed beverage ingredient is a promising cancer preventive agent. However, the relationship between green tea consumption and reduced cancer risk seen from epidemiologic studies is not as encouraging as that observed in animal studies and remains inconclusive. In the present article, the achievements using EGCG or green tea catechins for cancer prevention were reviewed, the latest identified anticancer mechanisms of EGCG and the emerging mechanism-based cancer therapies of EGCG were outlined, and the potential reasons for the discrepancy in animal studies and epidemiological studies were tentatively analysed. On the basis of these analyses, it could be anticipated that future intervention trials in humans would be able to achieve consistent cancer prevention effects provided that the timely intervention of EGCG or green tea catechins at appropriate high-dose levels presumably approaching their upper safety limits have had been fully considered.