Smart companies are working to better understand—and cut—those [greenhouse gas] emissions ahead of new regulations. The inaugural NEWSWEEK Green Rankings recognizes those efforts. For more than a year, the magazine worked with leading environmental researchers KLD Research & Analytics, Trucost, and CorporateRegister.com to rank the 500 largest U.S. companies based on their actual environmental performance, policies, and reputation. [refers to Intel, Wal-Mart, Marathon]