The chemistry of the vegetable tannins is examined with a discussion of their role in the biochemistry of plants. A table indicates the sources of vegetable tannins of commercial importance. Condensed tannins examined first are known as proanthocyanidins. Next are the hydrolyzable tannins, gallotannins, and ellagitannins. Considering their stability in the presence of water and known reactions with protein and oxygen, the changes likely to occur after prolonged aging are briefly discussed.