Plants form and emit a wide array of volatile organic chemicals. Some of them are important ingredients in foods as flavor, and the other attract us as ingredients in perfumes. Of course, plants from volatiles for their own sake. For reproductive organs, such as flowers or fruits, volatiles are essential to recruit pollinators and seed-dispersers. On the contrary, physiological significances of the volatiles formed in vegetative organs, such leaves, stems, or roots, have not been completely understood. I have been studying on volatile compounds, especially those formed from fatty acid, in leaves. I noticed that the volatiles mediate plant-microbe, and plant-plant interaction in ecosystems. Herewith I would like to present some example.