Merrill Monroe Jensen (July 16, 1905 in Elk Horn, Iowa – January 30, 1980 in Madison, Wisconsin) was an American historian, whose research and writing focused on the ratification of the United States Constitution. His historical interpretations are generally considered to be of the "Progressive School" of American history, the most famous exponent of which was Charles A. Beard. Jensen was a professor of history at the University of Washington (1935–1944), where he was editor of Pacific Northwest Quarterly, and the University of Wisconsin–Madison (1944–1976).