This chapter describes Toxic Substances Control Act (Tsca) and the roles of the TSCA Interagency Testing Committee, the US Environmental Protection Agency (EPA), and chemical manufacturers in recommending, implementing, and conducting aquatic toxicity, bioconcentration, and chemical fate testing under section 4 of TSCA. The Toxic Substances Control Act was promulgated in 1976 to regulate the manufacture, processing, use, transportation, or disposal of certain industrial chemical substances and to protect human health and the environment by requiring testing and necessary use restrictions on these chemical substances. The process is designed to save money in testing chemicals by obligating resources toward conducting only the most important tests based on the tested chemicals’ physical-chemical properties or structural characteristics. Congress intended that the “A” finding be applied to existing chemicals about which there is a basis for concern but for which there is inadequate information to reasonably determine or predict adverse effects.