Laurent Carl Siebenmann (the first name is sometimes spelled Laurence or Larry) (born 1939) 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 at the Centre national de la recherche scientifique in 1976.

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 Francis Bonahon and Albert Fathi.

In 1985 he was awarded the Jeffery–Williams Prize by the Canadian Mathematical Society.