Henri Léon Lebesgue (; June 28, 1875 – July 26, 1941) was a
French mathematician most famous for his
theory of integration, which was a generalization of the 17th century concept of integration—summing the area between an axis and the curve of a function defined for that axis. His theory was published originally in his dissertation
Intégrale, longueur, aire ("Integral, length, area") at the
University of Nancy during 1902.