The Leine is a river in Thuringia and Lower Saxony, Germany. It is a tributary of the Aller river and 241 km in length.

The river's source is located close to the town of Leinefelde in Thuringia. 40 km after the river enters Lower Saxony and runs northwards. Important towns on the course are Göttingen, Alfeld and Gronau, before the river enters Hanover, the largest city on the banks. Some 40 km north of Hanover the river joins the Aller.