To fully understand the contents of this book and the workshop from which it emanates, a review of activities which influenced the contents is helpful. The Toxic Substances Control Act (TSCA) was passed by Congress in October 1976, stipulating that no person may manufacture or process a chemical substance for a new use without obtaining clearance from the U. S. Environmental Protection Agency. TSCA represents an attempt to establish a mechanism whereby the hazard of a chemical substance to human health and the environment can be assessed before the chemical is introduced into the environment. In an effort to assist in the development of this conceptual framework for conducting an evaluation of the hazard of chemicals to aquatic life, an ad hoc workshop was conducted on 13-17 June 1977 at the University of Michigan’s Biological Station, Pellston, Mich., entitled "Application of Toxicity Testing Methods as Predictive Tools for Aquatic Safety Evaluation." The 1977 Pellston workshop and the 1978 Waterville Valley workshop were extremely useful in addressing state-of-the-art testing methods and hazard evaluation schemes. Both indicated the considerable effort was needed in the development of methods to predict the environmental fate of chemicals. For this reason, a thrid workshop was planned, organized, and conducted around the theme "Biotransformation and Fate of Chemicals in th eAquatic Environment." This workshop was held on 14-18 August 1979 at the University of Michigan’s Biological Station in Pellston; it focused on the methodology for biodegradation testing of chemicals and considered how predictive modeling contributes to fate determinations. The proceedings of this workshop constitute the contents of this book.