The core purpose of the Global Change Research Program in the U.S. Environmental Protection Agency (EPA) Office of Research and Development is to provide scientific information to stakeholders and policymakers to support them as they decide whether and how to respond to the risks and opportunities presented by global change. The program is stakeholder-oriented, with primary emphasis on assessing the potential consequences of global change (particularly climate variability and change) on air quality, water quality, aquatic ecosystems, and human health in the United States. The program’s focus on these four areas is driven by EPA’s mission and statutory and programmatic requirements. EPA uses the results of these studies to investigate adaptation options to improve society’s ability to effectively respond to the risks and opportunities presented by global change, and to develop decision-support tools for resource managers coping with a changing climate. EPA also has begun to invest in decision-support tools to help decision-makers evaluate alternative strategies for reducing greenhouse gas emissions and the environmental implications of those strategies.