Tea (Camellia sinensis, Theaceae) is one of the most widely consumed beverages in the world. The three major types of tea, green tea, oolong tea, and black tea, differ in terms of the manufacture and chemical composition. There are numerous studies in humans, animal models, and cell lines to suggest potential health benefits from the consumption of tea, including prevention of cancer and heart diseases. Many of the health benefits have been attributed to the polyphenolic constituents in tea. Catechins and their dimers (theaflavins) and polymers (thearubigins) have been identified as the major components in tea. Methylation, glucuronidation, sulfation, and ring-fission metabolism represent the major metabolic pathways for tea catechins. The present review summarizes the data concerning the chemistry and biotransformation of tea constituents. Copyright © 2011 Elsevier Ltd. All rights reserved.