Quercetin, the most common member of the flavonoids family, is a group of chemical compounds that can be found in the plant kingdom. Fruits and vegetables, particularly citrus fruits, apples, onions, parsley, tea, and red wine, are the primary dietary sources of quercetin. In this book, the authors present topical research in the study of the dietary sources, functions and health benefits of quercetin. Topics discussed include the formulations for pharmaceutical administration of quercetin; the action of quercetin on oxygen uptake by uncoupled mitochondria oxidizing various substrates; the oral health benefits of quercetin; in vitro antibacterial activities and murine studies of novel quercetin diacylglycosyde analogues and the suppressive effect of quercetin on intestinal tight junction permeability.