Rethen is a former municipality in the district of Gifhorn, Lower Saxony. The village was probably founded during the Saxon Wars of Charlemagne. In the Middle Ages, Rethen was a border town between the Roman Catholic Diocese of Hildesheim and Diocese of Halberstadt. In 1974 Rethen and Eickhorst were incorporated into the municipality of Vordorf, which belongs to the Samtgemeinde Papenteich. Today the village has about 1200 inhabitants.