Arendsee ( (help·info)) is a municipality in the Altmarkkreis Salzwedel, Saxony-Anhalt, Germany. It is named after the lake Arendsee, located north of the town.
The municipality is located in the Altmark region and on the southern bank of the Arendsee lake, the largest and deepest natural lake in Saxony-Anhalt.
The locality and the lake were first mentioned in the Royal Frankish Annals in 822.
In 1184 Otto I, Margrave of Brandenburg founded a Benedictine nunnery in Arendsee while the then competent Prince-Bishop of Verden, Tammo (d. 1188), endowed it with estates.