Incorporation of plant stanol esters into margarine is among the first examples of a functional food with proven low-density lipoprotein (LDL) cholesterol-lowering effectiveness. Recently, there have been many studies on the effects of plant stanols/sterols on cholesterol metabolism. It has been found that the serum LDL cholesterol-lowering effect of plant stanols/sterols originates from reduced intestinal cholesterol absorption, a process in which changes in micellar composition are thought to play a major role. However, recent findings suggest that there is an additional process in which plant stanols/sterols actively influence cellular cholesterol metabolism within intestinal enterocytes. Furthermore, in response to the reduced supply of exogenous cholesterol, receptor-mediated lipoprotein cholesterol uptake is probably enhanced, as shown by increased LDL receptor expression. At recommended intakes of about 2 to 2.5 g/day, products enriched with plant stanol/sterol esters lower plasma LDL cholesterol levels by 10% to 14% without any reported side effects. Thus, plant stanols/sterols can be considered to be effective and safe cholesterol-lowering functional food ingredients.