Nordborg (German: Norburg), is a town with a population of 5,729 (1 January 2024),[1] which was the seat of the former Nordborg municipality (Danish, kommune) in Sønderborg Municipality, Region of Southern Denmark on the northwest half of the island of Als off the east coast of the Jutland peninsula in south Denmark.

The town has been greatly influenced by the presence of Danfoss, a global producer of components for refrigeration and airconditioning, heating and motion control applications, headquartered in the town and founded in 1933.

The former Nordborg Municipality covered an area of 125 km2, and had a total population of 13,956 (2005).

Its last mayor was Jan Prokopek Jensen, a member of the Social Democrats (Socialdemokraterne) political party.

In later years, the municipality saw the rise of another major industrial company, Linak, a global producer of electric linear actuator systems.