American economist whose contributions to the theoretical formulation of investment behaviour offered valuable insights into financial markets. His work earned him the Nobel Prize for Economics in 1981.

After taking degrees from Harvard University (B.A., 1939; Ph.D., 1947), Tobin spent 1941–42 as an economist with the Office of Price Administration in Washington, D.C. During World War II he served in the Naval Reserve, rising to second in command of the destroyer USS Kearney. In 1950 he joined the faculty of Yale University, where in 1957 he became the Sterling Professor of Economics. In addition to teaching, he served as director of the Cowles Foundation for Research in Economics from 1955 to 1961 and again from 1964 to 1965.

Tobin, regarded by many as the most distinguished American Keynesian (Keynesian economics) economist, argued that monetary policy is effective in only one area—capital investment—and that interest rates are an important factor in capital investment but not the only one. He introduced “Tobin's q,” the ratio of the market value of an asset to its replacement cost. If an asset's q is greater than one, then new investment in similar assets will be profitable.

Tobin served as an adviser to Democratic presidential candidate George McGovern in 1972. Like many economists across the political spectrum, he pointed out the harmful consequences of government policies, such as the effect of a high minimum wage on the job prospects for inner-city youths. Tobin once wrote: “We should be especially suspicious of interventions that seem both inefficient and inequitable, for example, rent controls in New York or Moscow or Mexico City, or price supports and irrigation subsidies benefiting affluent farmers, or low-interest loans to well-heeled students.” Among his publications are The American Business Creed (with others, 1961), National Economic Policy (1966), Essays in Economics, 3 vol. (1971–82), and The New Economics One Decade Older (1974).