Fatty acids constitute the basic building material, from which human organisms draw structural compounds for their cells, tissues, and organs, as well as compounds to synthetize some biologically active substances. From among the fatty acids, the long-chain polyenic fatty acids are of the highest significance. The results of many studies have proved that polyenic fatty acids stimulate the cardiovascular system, as well as play a key role in the development of nervous system during intrauterine life and in early childhood. Based on the mode of action of polyenic fatty acids that has been explained, it will be possible to properly balance human diet in order to get and keep good health.