The benchmark for sustainable design in the United States is the Leadership in Energy and Environmental Design (LEED® ) rating system developed by the U.S. Green Building Council (USGBC). Through this system, buildings become LEED-certified by earning credits from the following categories: sustainable sites, water efficiency, energy and atmosphere, materials and resources, and indoor environmental quality. Only buildings can become LEED-certified – not products. When the United States Green Building Council introduced LEED in 1998, it made sustainability measurable.