Phytosterols are chemical homologs of cholesterol that are found in most plant foods and are particularly abundant in vegetable oils and whole grains. They interfere with the micellar solubilization of cholesterol in the intestine and reduce the efficiency of cholesterol absorption. The net absorption of phytosterols themselves is very small and most clinical studies suggest that consumption is safe. Phytosterols naturally present in foods appear to be bioactive, but many commercial phytosterol supplements are comprised of purified crystals with limited bioavailability. Proper formulation to improve bioavailability is critical for phytosterol supplements. Phytosterols appear to be quantitatively as important to cholesterol lowering as reducing saturated fat consumption, and they provide an additional tool for regulation of circulating cholesterol through lifestyle changes.