Publisher Summary This chapter explains the utility of zebrafish as a model for toxicological research. Zebrafish (Danio rerio) have long been the genetic model of choice for vertebrate developmental biologists, as it provides several advantages for investigating organ and tissue development. Zebrafish have become a powerful model organism for investigating the molecular and cellular mechanisms by which environmental chemicals disrupt normal developmental processes. The utility of zebrafish as a laboratory model organism also makes it an excellent system for studying processes in juvenile and adult organisms, including reproductive development, carcinogenesis, aging, and the influence of environmental chemicals on these processes. The advent of modern genetic tools and genome sequencing projects has elevated zebrafish as a suitable model to effectively study human disease and pathophysiology, ushering in a new era of comparative biology and medicine. The chapter reviews the mechanistic toxicology and advantages of the zebrafish model system.