The Leine (German: [ˈlaɪnə] ⓘ; Old Saxon Lagina) is a river in Thuringia and Lower Saxony, Germany.

Important towns along its course, from upstream to downstream, are Göttingen, Einbeck, Freden, Alfeld, and Gronau, before the river enters Hanover, the largest city on its banks.

Its northern (lower) 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.

Serial killer Fritz Haarmann disposed of most of his victims' remains in the Leine river.

[3] In his 1986 bestseller Red Storm Rising, author Tom Clancy uses the Leine as a major obstacle to the Soviet Union's Red Army drive to the Rhine and the North Sea ports of the Netherlands and Belgium through West Germany.