This book provides an overview of information and concepts about organic chemicals and contaminants that groundwater scientists and engineers should become familiar with to understand other books issued by The Groundwater Project as well as the scientific literature, government reports, government guidance, and consultants’ reports on groundwater contamination and remediation. It is written by university professors with specialties in groundwater contamination, remediation, field and laboratory experimentation, groundwater hydrogeology, chemical engineering, and computer simulation of groundwater transport and fate processes. All the authors taught graduate classes addressing the topics within this book and collaborated with many groundwater scientists on research projects to improve our knowledge of the processes that control groundwater transport and fate of contaminants. Their aim is to spark interest in the fascinating nature and fate of organic chemicals which have become broadly distributed in the environment, and lead readers to build on this knowledge to improve the management of these chemicals and reduce—ideally eliminate—the risks they pose.