The U.S. Environmental Protection Agency (EPA) Engineering Issues are a new series of technology transfer documents that summarize the latest available information on selected treatment and site re-mediation technologies and related issues. They are designed to help remedial project managers (RPMs), on-scene coordinators (OSCs), contractors, and other site managers understand the type of data and site characteristics needed to evaluate a technology for potential applicability to their specific sites. Each Engineering Issue document is developed in conjunction with a small group of scientists inside the EPA and with outside consultants and relies on peer-reviewed literature, EPA reports, Internet sources, current research, and other pertinent information. For this Engineering Issue paper, the reader is assumed to have a basic technical background and some familiarity with bioremediation. Those readers interested in a more basic discussion of bioremediation should consult the A Citizens Guide to Bioremediation (EPA, 2001a). The purpose of this Engineering Issue paper for biodegradation technologies is to summarize current information on bioremediation and to convey that information clearly and concisely to site managers.