Harrison Brown positioned his life's work at the intersection of science and public policy. Born in Wyoming, he received his BS in chemistry from Berkeley and his PhD in nuclear chemistry from Johns Hopkins in 1941. After working in the Manhattan Project, both at the University of Chicago and at Oak Ridge on the production of plutonium, Brown became an outspoken opponent of nuclear weapons. In 1947 he joined the Emergency Committee of Atomic Scientists and at the end of his life was the editor-in-chief of the Bulletin of the Atomic Scientists. He was the author or editor of more than ten books on social problems from the atomic bomb to the population explosion, including his most celebrated work, The Challenge of Man's Future (1954). He taught at the University of Chicago from 1946 to 1951, when he moved to Caltech, eventually holding a double appointment in the Geology and Humanities divisions. His early scientific studies on meteorites--for which he was awarded a prize in 1947 by the American Association for the Advancement of Science (AAAS)--were continued in along with work in mass spectroscopy, thermal diffusion, fluorine and plutonium chemistry, geochemistry and planetary structure. He served from 1962 to 1974 as foreign secretary of the National Academy of Sciences, as science adviser to the presidential campaigns of Adlai Stevenson and Robert Kennedy, and as delegate, advisor and committee member for numerous government, political and professional organizations.