Plants use metabolites to communicate with other organisms. This includes the production and emission of volatiles to repel harmful or to attract beneficial organisms, such as pollinators and natural enemies of herbivores. We are studying the regulation of the production of these chemical signals and use metabolic engineering approaches to try to underpin the biological role of individual signals. Also in the rhizosphere plants use volatile as well as non-volatile metabolites to communicate with enemies and friends. An exciting example of rhizosphere signalling molecules are the strigolactones. These are used by the friends of plants, the arbuscular mycorrhizal fungi, for host detection but also by plant enemies, root parasitic plants. Furthermore, they have an endogenous signalling function, as a plant hormone that regulates shoot branching and root architecture. Interestingly, there is large structural diversity in the strigolactones, with over 20 different compounds identified so far. The discovery of the multiple roles of the strigolactones will be discussed as well as the effect this may have on the evolution of diversity in their molecular structure and biological specificity.