Jan Denef (born 4 September 1951) is a Belgian mathematician. He is Professor of Mathematics at the Katholieke Universiteit Leuven (KULeuven).
He is a specialist of model theory, number theory and algebraic geometry. He is well known for his early work on Hilbert's tenth problem and for developing the theory of motivic integration in a series of papers with François Loeser. He has also worked on computational number theory.
Recently he proved a conjecture of Jean-Louis Colliot-Thélène which generalizes the Ax–Kochen theorem.
He was an invited speaker at ICM 2002. His Hirsch-index is 24.