Phenolic compounds or polyphenols constitute one of the most numerous and widely distributed group of substances in the plant kingdom. Polyphenolic compounds are closely associated to dietary fiber constituents and very often interfere with the analysis of this fraction of foods. Polyphenols are products of the secondary metabolism of plants, biogenetically arising from two main synthetic pathways: the shikimate pathway and the acetate pathway. The difficulty in the analysis of plant phenolics relates to the complete extraction of these compounds from the plant material. Polyphenols are polar compounds and moderately soluble in polar solvents such as ethanol, methanol, acetone, diethyl ether, and dimethyl sulfoxide. The nutritional significance of food phenolics will be greatly influenced by the behavior of polyphenols within the gastrointestinal tract. Extractable polyphenols are low and intermediate molecular weight phenolics that can be extracted using different solvents, including some hydrolyzable tannins and oligomeric proanthocyanidins.