The U.S. Environmental Protection Agency's Global Change Research Program (GCRP) is an assessment-oriented program within the Office of Research and Development that focuses on assessing how potential changes in climate and other global environmental stressors may impact water quality, air quality, aquatic ecosystems, and human health in the United States. The Program's focus on water quality is consistent with the Research Strategy of the U.S. Climate Change Research Program--the federal umbrella organization for climate change science in the U.S. government and is responsive to U.S. EPA's mission and responsibilities as defined by the Clean Water Act and the Safe Drinking Water Act. The GCRP's water quality assessments also address an important research gap. In the 2001 National Assessment of the Potential Consequences of Climate Change in the United States (Gleick, 2000), water quality was addressed only in the context of the health risks associated with contaminated drinking water. A comprehensive assessment of the potential impacts of global change on water quality was not included. This report is a screening-level assessment of the potential implications of future climate change on combined sewer overflows (CSOs) in the New England and the Great Lakes Regions.