John Marcus Fleming (1911 – February 3, 1976) was a British economist. He was the deputy director of the research department of the International Monetary Fund for many years; he was already a member of this department during the period of Canadian economist Robert Mundell's affiliation. At approximately the same time as Mundell, Fleming presented similar research on stabilization policy in open economies. As a result, today's textbooks refer to the Mundell–Fleming model. Mundell's contribution, which assumes perfect rather than imperfect capital mobility is, however, considered more important due to its depth, range, and analytical power, and more applicable to today's conditions.