William Arthur Niskanen (/nɪsˈkænən/; March 13, 1933 – October 26, 2011) was an American economist. He was one of the architects of President Ronald Reagan's economic program and contributed to public choice theory. He was also a long-time chairman of the Cato Institute, a libertarian think-tank.

Niskanen was born and raised in Bend, Oregon. He received his B.A. from Harvard University in 1954. He pursued graduate study of economics at the University of Chicago, where his teachers included Milton Friedman and other prominent economists who were then revolutionizing economics, public policy, and law with ideas that would come to be known as the Chicago school of economics. Niskanen received his M.A. in 1955 and his doctorate in 1962, writing his dissertation on the economics of alcoholic beverage sales.

After earning his doctoral degree, Niskanen joined the RAND Corporation as a defense policy analyst in 1957, using his economic and mathematical modeling skills to analyze and improve military efficiency. Among his accomplishments was developing a 400-line linear programming model of the Air Force transport system. His programmer for the model was a young William F. Sharpe, who would later win the Nobel economics prize.

Because of his work at RAND, the incoming Kennedy administration appointed Niskanen director of special studies in the Office of the Secretary of Defense. There, he became one of Defense Secretary Robert McNamara's original Pentagon "whiz kids" who used statistical analysis to examine Defense Department operations.

During his time at the Pentagon, Niskanen became disillusioned with the nation's political leadership, later claiming that the president and other executive branch officials "lied with ... regularity" to the public. He frequently quipped that this disillusionment sometimes caused him to question whether the United States truly landed on the moon in 1969.

Niskanen left DOD in 1964 to become director of the Program Analysis Division at the Institute for Defense Analyses. In 1972, he returned to public service as assistant director of the Office of Management and Budget, though his internal criticisms of Nixon administration policy would make his tenure at OMB short.

Niskanen left Washington and returned to academia, becoming professor of economics at the University of California at Berkeley in 1972, where he remained until he became chief economist of Ford Motor Company in 1975. While at Berkeley, Niskanen helped establish the school's graduate school of public policy. During this time in California, he became acquainted with then-governor Ronald Reagan, who appointed him to a task force on the state's economy.

Following his dismissal from Ford in 1980 (see below), Niskanen returned to academia, this time to UCLA.