Archibald Cary Coolidge (March 6, 1866 – January 14, 1928) was an American educator and diplomat. He was a Professor of History at Harvard College from 1908 and the first Director of the Harvard University Library from 1910 until his death. Coolidge was also a scholar in international affairs, a planner of the Widener Library, a member of the United States Foreign Service, and editor-in-chief of the policy journal Foreign Affairs.