Willi Jäger (born 15 August 1940 in Kschellowitz, Bohemia) is a German mathematician. He completed his PhD in 1966 the University of Munich under the direction of Erhard Heinz. From 1969 to 1970 Jäger was a visiting scientist at the Courant Institute in New York City. In 1970 he became professor of mathematics at the University of Münster and from 1974 he became professor of applied mathematics at the Heidelberg University. In 1987 Jäger was founding member of the Interdisciplinary Center for Scientific Computing in Heidelberg. He is a board member of the Mathematical Research Institute of Oberwolfach.