The Yonne is a tributary of the Seine in Burgundy-Franche-Comté and Île-de-France (France). The river is 293 km long and originates in the solid mass of the Morvan. The estuary in the Seine is at Montereau-Fault-Yonne. The Seine has covered a shorter distance than the Yonne until that point.
The Yonne is the name giver of the department of the Yonne, but also flows through the Nièvre and Seine-et-Marne departments. The main cities on the river are Auxerre and Sens.
The Yonne is navigable from Auxerre. The Burgundian Canal (opened in 1832) connects the river with the Saône and the Canal du Nivernais (1843) with the Loire.
In ancient times, the Yonne was known under the name Icaunus.