The role of natural terpenes stereochemistry is very important in the re-evaluation of established bioactivities of natural products. Thus, qualitative and/or quantitatives properties of stereoisomers are described from a point of view of food chemistry, chemical ecology, clinical medicine and pharmaceutical research. The new methodologies for stereoisomer studies are discussed. The enantiomeric excess in the production of chiral compounds both within nature and in the laboratory, is dependent not only on the intrinsic dynamics of the system but also on modulatory mechamisms imposed by the molecular environment. Moreover, stereospecificity becomes a relative concept when consired in conjuction with biodisponibility. The latters are the emerging problems which remain to be elucidated.