Polyphenols constitute one of the most numerous and ubiquitous groups of plant metabolites and are an integral part of both human and animal diets. The main polyphenol dietary sources are fruit and beverages (wine, tea, coffee, chocolate and beer) and to a lesser extent vegetables, dry legumes and cereals. Dietary polyphenols are mostly derivatives and/or isomers of flavones, isoflavones, flavonols, catechins and phenolic acids, and possess various biological properties. Research on the effects of dietary polyphenols on human health has developed strongly and supports a role for polyphenols in the prevention of degenerative diseases, particularly cardiovascular diseases, anti-inflammation, antiatherosclerosis, cardiovascular protection, improvement of the endothelial function, as well as inhibition of angiogenesis and cell proliferation activity. This paper covers the elaborate literature on the subject, and highlights the functions and protective effects of dietary polyphenols.