Laurent Carl Siebenmann (the first name is sometimes spelled Laurence or Larry) (born in 1939 in Toronto) is a Canadian mathematician based at the Université de Paris-Sud at Orsay, France. After working for several years as a Professor at Orsay he became a Directeur de Recherches in the French CNRS in 1976. He is an influential topologist who works on manifolds and who co-discovered the Kirby–Siebenmann class. His undergraduate studies were at the University of Toronto. He received a Ph.D. from Princeton University under the supervision of John Milnor in 1965 with the dissertation "The Obstruction to Finding a Boundary for an Open Manifold of Dimension Greater than Five". His doctoral students at Orsay included Michel Boileau, Francis Bonahon, Albert Fathi, Lucien Guillou, Alexis Marin and Jean-Pierre Otal. In 1985 he was awarded the Jeffery–Williams Prize by the Canadian Mathematical Society.