Flavonoids are polyphenolic secondary plant metabolites with a wide range of biological activities. There is an increasing awareness of the role of flavonoids as epidemiological studies suggest that consumption of flavonol- and isoflavone-rich diets may decrease the risk of developing coronary heart disease and certain cancers. Apart from some fermented foods and tea, where flavonoid aglycones are present, most of the dietary flavonoids are O-glycosides, mainly with D-glucose and in this form are ingested. As a rough estimate, the total daily intake of polyphenols is between 150 and 1000 mg. The paper is focused on the flavonoid (especially quercetin-related) metabolism. The processes involved are deglycosylation, transfer into enterocytes, glucuronidation, transport to liver via hepatic vein, or resecretion into intestinal lumen, further conjugation reactions in liver, enterohepatic recirculation, biliary and urinary excretion, metabolism by colonic microflora.