Paul Ledoux (8 August 1914 – 6 October 1988[2]) was a Belgian astrophysicist best known for his work on stellar stability and variability.

In stellar astrophysics, Ledoux's name is now associated with the criterion under which material in a star becomes unstable to convection in the presence of a gradient of chemical composition.

In homogeneous material, the Schwarzschild criterion shows that material is unstable to convection if the radiation field alone would establish a steeper temperature gradient steeper than the adiabatic (or isentropic) temperature gradient.

However, Ledoux showed that a composition gradient stabilises or destabilises the material against convection.

[5] In convectively-stable regions destabilised by the composition gradient, one expects thermohaline mixing; in convectively-unstable regions that are stabilised, one expects double-diffusive mixing, known in stellar astrophysics as semiconvection.