When it comes to understanding and improving the environment’s effects on health, few have had greater impact than HSPH alumnus and faculty member Douglas Dockery, SM ’74, SD ’79. Today, Dockery is chair of our Department of Environmental Health. But in the mid-1970s, he was a young researcher at the School about to embark on what would become a world-changing air pollution study. The so-called “Six Cities Study”—one of the single most influential research projects in public health history—found that the most polluted air in the U.S. translated to about a two-year loss in life expectancy. Work by Dockery and his colleagues paved the way for the nation’s Clean Air Act regulations on fine particulate matter and continues to influence air quality regulation around the world today. The Six Cities Study is also a textbook illustration of how public health should work: Good science shapes policy. Good policy saves lives.