Chemical Ecology is devoted to the study of substances that regulate interactions between plants, animals and microbes. Organisms communicate with each other by using chemical signals: Insects produce pheromones to alert conspecifics. When some plants are attacked, they release volatile substances which attract the enemies of the herbivores. There are insects that sequester chemicals from their host plants for their own defense. When insects smell volatiles from flowers or leaves or other animals, these odors may influence their behavior. Microorganisms, such as symbiotic bacteria, play an important part in many of these interactions. New insights into the development, behavior, reproduction, and co-evolution of the different organisms are used for environmental research and agriculture.