The Semois (known as the Semoy in France) is a river flowing from the Ardennes uplands of Belgium and France towards the Meuse, of which it is a right tributary.
The source of the Semois is in Arlon, Wallonia, in the Belgian province of Luxembourg, close to the border with the Grand Duchy of Luxembourg. Flowing in a roughly westerly direction, it enters France after passing through the Belgian village of Bohan-sur-Semois and forms about 2 kilometres (1.2 mi) of the Belgian–French border.
It joins the Meuse 24 kilometres (15 mi) further downstream in Monthermé.
The total length of the river is 210 kilometres (130 mi).
