The United States Department of Energy (DOE) has approximately 400 million liters (100 million gallons) of liquid high-level waste (HLW) stored in underground tanks and approximately 4,000 cubic meters of solid HLW stored in bins. The current DOE estimate of the cost of converting these liquid and solid wastes into stable forms for shipment to a geological repository exceeds $50 billion to be spent over several decades (DOE, 2000). This committee1 was appointed by the National Research Council (NRC) to advise the Environmental Management Science Program (EMSP)2 on a long-term research agenda addressing the above problems related to HLW3 stored in tanks and bins at DOE sites.4 The complete statement of task is reproduced in Sidebar P.1 of the Preface. The committee outlined HLW problem areas that either cannot be addressed effectively with current technologies, or that are anticipated for the future. From these problem areas, the committee identified research objectives, leaving to EMSP investigators the role of determining the pathway to achieving these objectives through basic research. Moreover, it is not the purpose of this report to circumscribe the investigatorsŐ creativity by giving a detailed list of research projects.