The Leine is a river in Thuringia and Lower Saxony, Germany. It is a left tributary of the Aller and the Weser and it is 281 km long.
The river's source is located close to the town of Leinefelde in Thuringia. About 40 km downriver, the river enters Lower Saxony and runs northwards.
Important towns along its course, from upstream to downstream, are Göttingen, Einbeck, Alfeld, and Gronau, before the river enters Hanover, the largest city on its banks. Downstream some 40 km north of Hanover, near Schwarmstedt, the river joins the Aller and reaches the North Sea via the Weser. Its northern reaches are only navigable today by the smallest commercial carriers, though in the past, it served as an important pre-railway barge transport artery as far upriver as Göttingen.
The river is somewhat polluted by industry, so the water is not used for drinking, but the pollution has never been severe enough to prevent fish from living in it. Like many western rivers since the 1960s, it has enjoyed increasingly cleaner waters since the implementation of environmental controls. Sport fishing is enjoyed from small boats and along the banks, although yields are normally low.