Rendsburg is a town on the River Eider and the Kiel Canal in the central part of Schleswig-Holstein, Germany. It is the capital of the Kreis (district) of Rendsburg-Eckernförde. As of 2006, it had a population of 28,476.

The Eider is the longest river in the German state of Schleswig-Holstein. The river starts near Bordesholm and reaches the southwestern outskirts of Kiel on the shores of the Baltic Sea, but flows to the west, ending in the North Sea. The lower part of the Eider was used as part of the Eider Canal until that canal was replaced by the modern Kiel Canal.