Research to provide the scientific foundation for environmental decision making is a vital part of the U.S. Environmental Protection Agency's (EPA's) mission. To be effective, environmental research must continually evolve in response to changes in scientific understanding of the nature and complexity of environmental problems. In recent years, EPA has been reexamining the structure and focus of its research as part of an ongoing effort to improve the quality of its science and to expand the range, efficiency, and effectiveness of the approaches and tools available to mitigate and solve our nation's environmental problems. To assist in this reexamination, EPA called upon two independent advisory groups: the Science Advisory Board and the Expert Panel on the Role of Science at EPA. In response to their recommendations and to new policy directions within the Agency, EPA's Office of Research and Development has redesigned both the content and structure of its research programs to produce a comprehensive, integrated, and targeted research agenda that can more effectively respond to the environmental decision making needs of the coming years.