Nordborg, is a town with a population of 5,759, which was the seat of the former Nordborg municipality 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.

Sønderborg Municipality, is a kommune in the Region of Southern Denmark partially on the Jutland peninsula and partially on the island of Als in south Denmark, at the border with Germany. The municipality covers an area of 495.86 km2 (191.45 sq mi), and has a population of 74,380. Its mayor as of 1 January 2014 is Erik Lauritzen, a member of the Social Democratic party.