Insecticides are substances used to kill insects. They are used primarily in agriculture to control pests that infest crop. Nearly all insecticides have the potential to significantly alter ecosystems: many are toxic to humans and/or animals; some become concentrated as they spread along the food chain. The presence of these chemicals in both aquatic and terrestrial ecosystems has become an important issue globally. The book Insecticides - Agriculture and Toxicology provides information on the use of insecticides in pest management in order to enhance crop protection and their effects on nontarget organisms.