René Benoît (28.11.1844-4.05.1922) was a French physicist and a member of the Paris Academy of Sciences (1903). He was born in Montpellier, where he graduated (1869) from the medical school. In 1873 he received the degree of doctor at Nantes. From 1878 he worked at the International Bureau of Weights and Measures at Sèvres (director in 1889-1915). His work was in the fields of electricity, optics, heat and mechanics. He played a large part in the standardisation of the units of length, temperature and electrical resistance. He established the relation between the standard metre and the wavelength of light, measuring in 1907, together with Ch. Fabry and A. Perot, the wavelength of the red line of cadmium. He studied the motion of the pendulum, the electrical resistance of metals and its dependence on temperature, and the international ohm. He was president of the French Physical Society.