Phenolic and polyphenolic compounds in foods and natural nutraceutical products represent the most widely distributed plant secondary metabolites exerting their beneficial effects as free radical scavengers and chelators of pro-oxidant metals and thus preventing low-density lipoprotein oxidation and DNA strand scission or enhancing immune function. Phenolic compounds have been shown to control certain types of cancer, cardiovascular disease and the process of aging. This book reports the chemistry and analysis of phenolic compounds in various foods such as wheat brans, canola hulls, blueberry leaf, sesame, edible oil seeds and honeybush tea. Extensive coverage was given to green and black tea. The chemistry of the production of black tea theaflavins, the action mechanisms of theaflavins on anti-tumor effects, the anti-inflammatory activity of theaflavin, the bioavailability and biotransformation of tea polyphenols, and a practical example on the use of tea catechin as foodantioxidant and antibacterial were presented. Anticancer effects of other polyphenols from apple, cranberry and spices are also discussed.