Théophile Ernest de Donder (French: [də dɔ̃dɛʁ]; 19 August 1872 – 11 May 1957) was a Belgian mathematician, physicist and chemist famous for his work (published in 1923) in developing correlations between the Newtonian concept of chemical affinity and the Gibbsian concept of free energy.

He received his doctorate in physics and mathematics from the Université Libre de Bruxelles in 1899, for a thesis entitled Sur la Théorie des Invariants Intégraux (On the Theory of Integral Invariants).

From 1914 on, he was influenced by the work of Albert Einstein and was an enthusiastic proponent of the theory of relativity.

He gained significant reputation in 1923, when he developed his definition of chemical affinity.

He pointed out a connection between the chemical affinity and the Gibbs free energy.