The Grand Morin (French pronunciation: [ɡʁɑ̃ mɔʁɛ̃], literally Great Morin) is a 118-kilometre (73 mi) long river in France, left tributary of the Marne.^[1] Its source is near the village of Lachy. Its course crosses the departments of Marne and Seine-et-Marne. It flows westwards through the towns of Esternay, La Ferté-Gaucher, Coulommiers and Crécy-la-Chapelle, finally flowing into the Marne in Esbly.

Its main tributary is the Aubetin.