Throughout the United States, Americans are taking action to address the grave challenge of climate change, and to promote a sustainable and prosperous clean energy future. These efforts are occurring at all levels of government, in the private sector, and through the everyday decisions of individual citizens. This U.S. Climate Action Report 2010 sets out the major actions the U.S. government is taking at the federal level, highlights examples of state and local actions, and outlines U.S. efforts to assist other countries' efforts to address climate change. This 2010 CAR, submitted as a formal national communication, in accordance with Articles 4 and 12 of the UNFCCC, documents the actions the United States is taking to address climate change. This review accounts for current and proposed activities up to 2010. This report cites information and data available through 2009, except under very special circumstances, where more recent data were available. It explains how U.S. social, economic, and geographic circumstances affect U.S. GHG emissions, summarizes U.S. GHG emission trends from 1990 through 2007, identifies existing and planned U.S. policies and measures to reduce GHGs, and reports, wherever possible, measurable and verifiable emission reduction estimates for those policies and measures. The report also indicates future trends for U.S. GHG emissions, outlines the impacts of climate change on the United States and the adaptation measures the nation is taking to address those impacts, provides information on climate-related financial resources and technology transfer, details U.S. research and systematic observation efforts, and describes U.S. climate education, training, and outreach initiatives.