Hardegsen (German pronunciation: [ˈhaːɐ̯.dɛksn̩] ⓘ) is a town in the district of Northeim, in Lower Saxony, Germany.

In the end of the 14th century the castle passed to Otto von Braunschweig zu Göttingen.

In the end of the 18th century, Burg Hardeg, once a princely castle, was stripped of its former luxuries and converted into a farmhouse .

In 1972 the business vacated the castle, and its management passed to the municipality and local preservation society.

Solling Railway connects Hardegsen with Northeim and the southern part of Solling-Vogler Nature Park.