RENDSBURG, a town of Germany, in the Prussian province of Schleswig-Holstein, situated on the Eider and on the Kaiser Wilhelm canal, in a flat and sandy district, 20 m. W. of Kiel, on the Altona-Vamdrup railway. Pop. (1905) 15,577. It consists of three parts-the crowded Altstadt, on an island in the Eider; the Neuwerk, on the south bank of the river; and the Kronwerk, on the north bank.

Rendsburg is the chief place in the basin of the Eider, and when in the possession of Denmark was maintained as a fortress. Its present importance, however, rests on the commercial facilities afforded by its connexion with the North Sea and the Baltic through the Kaiser Wilhelm canal, by which transit trade is carried on in grain, timber, Swedish iron and coals. The principal industries are cotton-weaving, tanning and the manufacture of artificial manures. Rendsburg came into existence under the shelter of a castle founded by the Danes about the year 1100 on an island of the Eider, and was an object of dispute between the Danish kings and the counts of Holstein. In 1252 it was adjudged to the latter. The town was surrounded with ramparts in 1539, but the fortifications of the Kronwerk were not constructed till the end of the 17th century. During the Thirty Years' War Rendsburg was taken both by the Imperialists and the Swedes, but in 1645 it successfully resisted a second siege by the latter.

The war of 1848–50 began with the capture of Rendsburg by the Holsteiners by a coup de main, and it formed the centre of the German operations. On the departure of the German troops in 1852 the Danes demolished the fortifications on the north side. Immediately after the death of King Frederick VII. (15th of November 1863) the town was occupied by the Saxon troops acting as the executive of the German Confederation, and it was the base of the operations of the Austrians and Prussians against Schleswig in the spring of the following year. On the termination of the Danish war in 1864 Rendsburg was jointly occupied by Austrian and Prussian military until 1866, when it fell to Prussia.

See Warmstedt, Rendsburg (Kiel, 1850).