Louis "Marcel" Brillouin (19 December 1854 - 16 June 1948) was a French physicist and mathematician who made a significant contribution to the development of quantum mechanics. Born in Melle, Deux-Sèvres, France, his father was a painter who moved to Paris when Marcel was a boy. There he attended the Lycée Condorcet. The Brillouin family returned to Melle during the Franco-Prussian War of 1870 to escape the fighting. There he spent time teaching himself from his grandfather's philosophy books. After the war, he returned to Paris and entered the École Normale Supérieure in 1874 and graduated in 1878. He became a physics assistant at the Collège de France, while at the same time working for his doctorate in mathematics and physics, which he gained in 1881. Brillouin then held successive posts as assistant professor of physics at universities in Nancy, Dijon and Toulouse before returning to the École Normale Supérieure in Paris in 1888. Later, he was Professor of Mathematical Physics at the Collège de France from 1900 to 1931. During his career he was the author of over 200 experimental and theoretic papers on a wide range of topics which include the kinetic theory of gases, viscosity, thermodynamics, electricity, and the physics of melting conditions. Most notably he: built a new model of the Eötvös balance, wrote on Helmholtz flow and the stability of aircraft, worked on the atomic structure of the Niels Bohr model of the atom. His results here were later used by de Broglie and Schrödinger, worked on a theory of the tides. His son Léon Brillouin, also had a prominent career in physics.