Over the past decade, the possibility of using phytosterols as ingredients in functional foods has led to numerous research studies in relation to their ability to reduce blood cholesterol. Many different types of carriers have been tested, with good results. The main conclusion is that the effective doses were between 1.5 and 3g/day, leading to reductions between 8% and 15% in LDL-cholesterol. The principal mechanism of action is based on interference with the solubilisation of the cholesterol in the intestinal micelles and, thus, absorption is reduced. Work has also been done on the optimal pattern of administration, and it has been found that ingesting phytosterols in a single dose per day or between meals are equally effective methods. The only side effect is that they can interfere with the absorption of carotenoids, but this can be compensated for in the diet or by adding these compounds in appropriate carriers. It has also been reported that phytosterols have anticancer properties and act as immune system modulators. There are several possible future lines of research: alternative sources with a high phytosterol content must be found, industrial processes must be implemented which minimise their loss, phytosterols must be included in food composition tables, the potential of the different types of phytosterols must be discerned, the genetic bases of their action must be elucidated, synergic effects with other compounds must be studied, side effects must be minimised, and the effects of long-term treatment must be defined precisely.