Alvin Harvey Hansen (August 23, 1887, Viborg, South Dakota - Alexandria, Virginia, June 6, 1975) was an American economist and professor who developed the ideas of John Maynard Keynes in the United States and served as a special advisor to the highest-ranking economic organizations in his country.

Graduated from Yankton College in South Dakota in 1910, he worked as an educator and then studied at the University of Wisconsin-Madison where he earned a doctorate in Economics in 1918. He then taught at Brown University and the University of Minnesota. During this period his works were still part of neoclassical economic concepts. In 1937 he was appointed professor of political economy at Harvard University, where he approached Keynesian theory. His seminar on budget policy featured students such as Paul Samuelson and James Tobin, who later popularized Keynes' theories. Hansen's book Fiscal Policy and the Business Cycle (1941) was the first major academic work to accept Keynesian analysis of the Great Depression and support public investment activities in the United States. Hansen was vice president of the American Statistical Association and president of the American Economic Association.

During the administrations of Presidents Roosevelt and Truman, Hansen played an important role in the design of economic policies, was a member of numerous government commissions and a consultant to the Federal Reserve, the United States Department of the Treasury and the National Resources Planning Board. In 1935 he participated in the creation of the American social security system and in 1946 he was one of the drafters of the Full Employment Act which, among other things, created the Council of Economic Advisors.

Hansen's most notable contribution to economic theory was the joint development with John Hicks of the so-called IS-LM Model, also known as the Hicks-Hansen Synthesis. This scheme represents the relationships between investment-savings (IS) and the money supply (LM) and is used to illustrate how monetary and budgetary policies can influence GDP.