Walter Yasuo Oi (July 1, 1929 – December 24, 2013) was the Elmer B. Milliman Professor of Economics at the University of Rochester in Rochester, New York. He was a fellow of the American Academy of Arts and Sciences, a distinguished fellow of the Society of Labor Economists, and a recipient of the Secretary of Defense Medal for Outstanding Public Service. He is credited with providing the economic basis for a voluntary military and the elimination of a draft.