Louis-Paul Cailletet (1832 - 1913) was a French physicist and inventor.

He was born in Châtillon-sur-Seine, France.

He succeeded in producing droplets of liquid oxygen in 1877 but by a different method from that used by Raoul Pictet. He used the Joule-Thomson effect. The oxygen was compressed whilst being cooled. The compressed gas was then allowed to expand rapidly, cooling it even more. The result was the production of small droplets of liquid oxygen.