To find the greenest states (and the least green), Forbes ranked them on a per-capita basis in six equally weighted categories: carbon footprint, air quality, water quality, hazardous waste management, policy initiatives and energy consumption using the most recent data available from the following sources: the American Lung Association's 2007 State of the Air Report, American Council for an Energy-Efficient Economy's energy efficiency scorecard, U.S. Green Building Council, the Energy Information Administration, the Environmental Protection Agency, Department of Transportation, the Natural Resources Defense Council, the U.S. Public Interest Research Group and the Sierra Club.