Proanthocyanidins, also called condensed tannins, are oligomers and polymers of monomeric flavonoids. More specifically, they are polyflavans, condensed molecules of those flavonoids with a saturated ‘‘C’’ ring (Fig. 1A). Fifteen subclasses of proanthocyanidins have been identified;[1] however, only a few are prominent in foods and supplements of plant origin. The various subclasses are named based on the conversion of the ‘‘interior’’ monomeric units (M) to the corresponding anthocyanidin during acid catalyzed depolymerization. Hence, this broad class of polymers is named proanthocyanidins. Examples include conversion of (epi)catechin to cyanidin (procyanidins) and (epi)gallocatechin to delphinidin (prodelphinidins). In these tannins, the monomeric units are primarily linked through single 4! 6 or 4! 8 carbon-carbon bonds (B linkages), or through 4! 8 carbon-carbon and 2! 7 ether bonds (A linkages) (Fig. 1). Other linkages have also been identified, but have been isolated from nonfood plants or constitute minor compounds of foods such as cocoa.[1] Proanthocyanidins range in size from dimers through very large polymers and are found in many plant based foods and several dietary supplements.