Quercetin, one of the most taken flavonoid with diet, belongs to the family of flavonols in which kaempferol and myricetin are also found. Quercetin occurs as a glycoside (with linked sugars) or as an aglycone (without linked sugars). Although quercetin has many different forms in nature, the form found in plants is quercetin-3-O-glucoside, which generally functions as a pigment that gives color to a multitude of fruits and vegetables. The recent literature has been reviewed using PubMed, Science Direct, and Embase databases. In this article, we reviewed quercetin with respect to chemical properties, absorption mechanism, metabolism, bioavailability, food sources, bioactivities, and possible health-promoting mechanisms. Quercetin is known as an antioxidant, anti-inflammatory, cardioprotective, and anti-obesity compound. It is thought to be beneficial against cardiovascular diseases, cancer, diabetes, neurological diseases, obesity, allergy asthma, and atopic diseases. Further clinical studies with large sample sizes are needed to determine the appropriate dose and form of quercetin for preventing diseases.