This volume of Reviews in Environmental Contamination and Toxicology (RECT) is devoted to an ecological risk assessment of the insecticide, chlorpyrifos (CPY). Chlorpyrifos ( O , O -diethyl O -(3,5,6-trichloro-2-pyridinyl) phosphorothioate; CAS No. 2921-88-2) is a widely used organophosphorus insecticide that is impor- tant for the control of a large number of insect pests of crops. Applications are made to soil or foliage and can occur pre-plant, at-plant, post-plant, or during the dormant season.