The Marne is a river in France, a tributary of the Seine in the area east and southeast of Paris. It is about 525 km (326 mi) long. The river gave its name to the départements of Haute-Marne, Marne, Seine-et-Marne, and Val-de-Marne.

The Marne starts in the Langres plateau, runs generally north then bends west between Saint-Dizier and Châlons-en-Champagne, joining the Seine at Charenton just upstream from Paris.

The Marne River was the site of two battles during the First World War. The first battle was the turning point of World War I, fought in 1914. The second battle was fought four years later, in 1918.