The US Department of Energy's Office of Civilian Radioactive Waste Management (OCRWM) is responsible for obtaining regulatory approval to construct and operate a spent nuclear fuel and high-level waste geologic repository at Yucca Mountain and to develop transportation and infrastructure needed to support operations. Most OCRWM program resources are devoted to these important objectives, to be accomplished over a long time frame. OCRWM has also begun a separate science and technology initiative to develop technological improvements and system enhancements to its baseline practices. Our overview of the technical content of this Science and Technology Program summarizes its rationale, beginnings, areas of current investigation, and near-term plans. In 2002, following a national decision-making process specified in the 1982 Nuclear Waste Policy Act, Yucca Mountain was formally designated as the site for the nation's geologic repository for commercial spent fuel and HLW generated from defense programs. By transporting spent fuel and HLW safely to Yucca Mountain for emplacement underground, OCRWM will fulfill its mission ''to manage and dispose of high-level radioactive waste and spent nuclear fuel in a manner that protects health, safety, and the environment; enhances national and energy security; and merits public confidence''. The activities involved in accepting, transporting, handling,more » and disposing of spent fuel and other HLW are planned to span decades, if not centuries, and hence many components of the waste management system (e.g., spent fuel handling facilities and the Yucca Mountain repository itself) are designed for long-term operations. Current plans adequately address all system requirements using present-day technology, but relevant technical advances (in both scientific knowledge and engineering practice) will continue over time.« less