Ahrensburg (German pronunciation: [ˈaːʁənsˌbʊʁk] ⓘ) is a town in the district of Stormarn, Schleswig-Holstein, Germany.

Ahrensburg is situated in the Tunneltal, in which Alfred Rust excavated many items dating back to the ice age.

Ahrensburg is situated next to the Autobahn A1 and on the railway route between the Hanseatic cities of Hamburg and Lübeck.

The village came into the possession of the Cistercian Reinfeld Abbey in 1327, and Woldenhorn became the seat of the monastery reeve until the middle of the 16th century.

The Rantzaus' estate was heavily indebted by the middle of the 18th century and, in 1759, was acquired by the businessman Heinrich Carl von Schimmelmann.

Schimmelmann remodelled the castle and village in the baroque style and the current layout of the town reflects these plans.

When Ahrensburg received city rights in 1949, the town had some 17,775 inhabitants – around half of which were refugees from the former eastern German regions.