The Aisne (n/; French: [ɛːn]) is a river in northeastern France. It is a left tributary of the Oise. It gave its name to the French department of Aisne. It was known in the Roman period as Axona.
It rises in the forest of Argonne, at Rembercourt-Sommaisne, near Sainte-Menehould. It flows north and then west before joining the Oise near Compiègne. The Aisne is 356 kilometres (221 mi) long. Its main tributaries are the Vesle, the Aire and the Suippe. Three Battles of the Aisne were fought in the Aisne valley during the First World War.
Departments and towns along the river include: