Rethen (Leine) is a part of the town of Laatzen in the district of Hanover, in Lower Saxony, Germany.

In 1523, Rethen coincided with the Koldingen Office to the Duchy of Calenberg.

The construction of the railway line Hanover-Kassel (operation 1853) brought a significant upswing, which intensified again from March 22, 1899, by the inclusion of the tram from Hanover to Hildesheim.

The modern transportation promoted several industrial settlements, including the sugar factory in 1876, which had a long time national significance.

In 1974 Rethen lost its independency and was merged with the towns of Gleidingen, Grasdorf, Alt-Laatzen, Laatzen Mitte and Ingeln-Oesselse to the city of Laatzen.