The accumulation of large amounts of ash from fossil fuel combustion for electric power generation is becoming a major environmental concern in the United States. Fur­ thermore, stringent environmental requirements mandated by the Environmental Pro­ tection Agency including the Clean Air Act, Clean Water Act, Resource Conservation and Recovery Act as well as state and local environmental regulations may result in even more ash production with subsequent contact with the environment. The concentrations of trace elements in coal residues are extremely variable and depend on the composition of the original coal, conditions during combustion, the efficiency of emission control devices, storage and handling of by-products, and climate. The research papers in this book were presented as a part of the Fourth International Conferenceon theBiogeochemistryofTrace Elements heldat Clark-KerrCampus, University of California at Berkeley, California during June 1997. The purpose of the conference was to present current knowledge on the sources, pathways, behavior and effects of trace elements in soils, waters, plants and animals. In addition, the book also includes invited research papers from scientists who have done significant research work in the area of coal and coal combustion byproducts. All the research paper presented herein have been subjected to peer review.