David Easton (June 24, 1917 – July 19, 2014) was a Canadian-born American political scientist. Easton, who was born in Toronto, Ontario, came to the United States in 1943. From 1947 to 1997, he served as a professor of political science at the University of Chicago. At the forefront of both the behavioralist and post-behavioralist revolutions in the discipline of political science during the 1950s and 1970s, Easton provided the discipline's most widely used definition of politics as the authoritative allocation of values for the society. He is renowned for his application of systems theory to the study of political science. Policy analysts have utilized his five-fold scheme for studying the policy-making process: input, conversion, output, feedback and environment. Gunnell argues that since the 1950s the concept of "system" was the most important theoretical concept used by American political scientists. The idea appeared in sociology and other social sciences but it was Easton who specified how it could be best applied to behavioral research on politics.During his career he served as a key gatekeeper, as consultant to many prominent organizations and funding agencies, and author of numerous influential scholarly publications. He served on many boards and committees and was president of the American Political Science Association.