"We're number three! We're number three!" Not quite a popular chant at most sporting events. But it is a proud declaration if you're talking about the 50 greenest cities in America. Popular Science used the raw data from the U.S. Census Bureau and the National Geographic Society’s Green Guide and put these numbers into four broad categories—electricity, transportation, green living, and recycling and green perspective—to determine each of the city’s rankings. And Boston came out #3! Check out the entire list here, as well as six case studies on how the greenest cities are cleaning up.