Polyphenols are substances of plant origin that occur in numerous fruits and vegetables, wine, tea, olive oil, chocolate and other cocoa products. They show antioxidant properties in vitro and many of their biological actions have been attributed to their intrinsic reducing capabilities. Research on the effects of dietary polyphenols on human health has developed considerably in the past 10 years. It strongly supports a role for polyphenols in the prevention of degenerative diseases, particularly cardiovascular diseases, osteoporosis, neurodegenerative, diabetes mellitus and cancers. The antioxidant properties of polyphenols have been widely studied, but it has become clear that the mechanisms of action of polyphenols go beyond the modulation of oxidative stress. Polyphenols are currently sold as nutritional supplements. Yet the scientific basis for the health claims for polyphenols is mostly weak. Results from in vitro studies are often directly translated into possible beneficial health effects in humans. However, in the body, polyphenols are quickly and easily converted into polyphenol metabolites. Presented review on Polyphenols and Health, offers an overview of the experimental, clinical and epidemiologic evidence of the effects of polyphenols on health.