Most people would know that a green building must be an energy efficient building. But not everyone agrees on how to define and measure efficiency. The Eviromental Protection Agency Guiding Principles for Federal Leadership in High Performance and Sustainable Buildings, recently adopted by over 18 federal agencies, including the EPA, provide a good model. The Guiding Principles call for integrated design, energy performance, water conservation, indoor environmental quality, and materials aimed at helping Federal agencies and organizations.