During the last century, researchers have focused on the influence of certain chemicals involved in interactions between living organisms. The production or biosynthesis of such organic compounds and their distribution between the producers or between other organisms are important questions in chemical ecology. The response to signalling molecules, the effects of certain toxins and especially the interactions between different kingdoms, such as insect-plant interactions, fungi-plant nteractions or plant-plant interactions, represent major research topics of this field. Over their entire lifetime, plants are exposed to a variety of stress factors. Such stress factors can be either abiotic or biotic. Abiotic stress is caused by environmental factors, such as water deficit, extreme temperature or light conditions. Biotic stress is caused by different living organisms, such as herbivores, pathogens or fungi. Stress affects plants in their development and reproduction processes. Since they are unable to move, they have evolved efficient strategies to cope with or to adapt to such stresses. Plants have developed a wide range of defensive mechanisms to survive and fight against attacking enemies. Recognition of enemies and the triggered answer cascade is part of the study of chemical ecology as well.