Tea, made from the leaves of the plant Camellia sinensis, Theaceae, is a popular beverage worldwide. For the past 30 years, tea has been studied extensively for its beneficial health effects in the prevention of cancer, diabetes, cardiovascular diseases and neurodegenerative diseases; reduction of body weight; and alleviation of metabolic syndrome. Whereas results from laboratory studies on these effects are strong, human studies have demonstrated the beneficial effects only in certain diseases in individuals who consume three to four or more cups of tea daily. This chapter reviews these beneficial health effects of tea, the possible mechanisms of actions of tea constituents, and the relevance of laboratory studies to human health.