AOP diagram“Adverse Outcome Pathways: Development and Use in Toxicology,” a chapter in Elsevier’s Encyclopedia of Toxicology (3rd edition) written by HSUS/HTPC’s Dr. Catherine Willett, introduces readers to the concept of Adverse Outcome Pathways (AOP) and explains how they can improve the efficiency and accuracy of toxicity testing while reducing the use of animals.  Dr. Willett’s chapter discusses how to construct an AOP, explores possible regulatory uses, and includes descriptions of two AOPs currently under development by the international research community.