Alvin Harvey Hansen (1887-1975) was a business cycle theorist who, in the late 1930s, became one of the leading exponents of Keynesian thinking, seeing the Keynes’s multiplier as providing a missing link in his earlier, dynamic theory of the cycle. After moving from Minnesota to Harvard in 1937, together with John Williams, he ran the Fiscal Policy Seminar, which was an important forum in which young economists debated Keynesian ideas. His Guide to Keynes offered the canonical statement of what became known as the IS-LM model.