Green tea (GT) is a beverage derived from the unfermented leaves of Camellia sinensis, a plant native to Asia. Green tea extract is marketed as an antioxidant and dietary supplement to support cardiovascular, metabolic, cognitive, and cellular health. Data on the use of GT in oncology are controversial, mainly because of the risk of interference with anticancer drugs. To date, the use of GT is recommended as supportive treatment in most oncological diseases.