Aimé Auguste Cotton (9 October 1869 – 16 April 1951) was a French physicist known for his studies of the interaction of light with chiral molecules.

In the absorption bands of these molecules, he discovered large values of optical rotatory dispersion (ORD), or variation of optical rotation as a function of wavelength (Cotton effect), as well as circular dichroism or differences of absorption between left and right circularly polarized light.

In 1904 he was appointed instructor, and in 1910 assistant professor at the science faculty of the University of Paris, assigned to the École normale supérieure, where he remained until 1922.

He worked first with Pierre Weiss on the Zeeman effect, the splitting of spectral lines in the presence of a magnetic field.

With Weiss he studied the magnetic splitting of the blue lines of the zinc atom and in 1907 they were able to determine the ratio of the electron's charge to its mass (e/m) with better precision than the method of J.J. Thomson.

During World War I he and Pierre Weiss developed the Cotton–Weiss system, based on an acoustic method, for locating enemy artillery.

Also, in 1941 he was imprisoned by the German occupiers at Fresnes for one and a half months and was later awarded the Rosette de la résistance.