To fully evaluate the potential risks and benefits of isoflavones to human health, an understanding of the physiological behavior of these compounds following ingestion is required. Numerous researchers have investigated the kinetics and extent of polyphenol absorption by measuring plasma concentrations and/or urinary excretion among adults after the ingestion of a single dose of polyphenol, provided as either a pure compound, plant extract, or whole food/beverage. Available data suggest isoflavones are more bioavailable than other flavonoid subclasses. This review will focus on our current understanding of factors affecting isoflavone absorption and metabolism in humans.