Jean-Marc Fontaine (13 March 1944 – 29 January 2019) was a French mathematician.

In 1962 Fontaine entered the École Polytechnique, from 1965 to 1971 was a researcher at CNRS and received his doctorate in 1972.

He proved that there are no non-trivial abelian varieties over the rational numbers with good reduction everywhere (Il n'y a pas de variété abélienne sur Z, Inventiones Mathematicae vol.

In 1984 he received the Prix Carrière from the French Academy of Sciences.

His students included Christophe Breuil, Pierre Colmez, and Jean-Pierre Wintenberger.