Johan Frederik Steffensen (1873–1961) was a Danish mathematician, statistician, and actuary who did research in the fields of calculus of finite differences and interpolation. He was professor of actuarial science at the University of Copenhagen from 1923 to 1943. Steffensen's inequality and Steffensen's method (an iterative numerical method) are named after him.
N. E. Nordlund, Johan Frederik Steffensen in memoriam, Nordisk Matematisk Tidsskrift, 10 (1962) 105-107.