| Diemel | |
| Map: | Diemel.png |
| Source1 Coordinates: | 51.2664°N 8.6514°W |
| Mouth Coordinates: | 51.6425°N 9.4478°W |
| Subdivision Type1: | Country |
| Length: | 110.4km (68.6miles) |
| Source1 Elevation: | 680m (2,230feet) |
| Basin Size: | 1762km2 |
| Tributaries Right: | Twiste |
The Diemel is a river in Hesse and North Rhine-Westphalia, Germany. It is a western and orographically left tributary of the Weser. It is the first, and therefore southernmost, of the larger Weser tributaries after its formation by the confluence of the Fulda and Werra rivers.
The source of the Diemel is near Willingen, in Sauerland. The Diemel flows generally northeast through the towns Marsberg, Warburg, and Trendelburg. It flows into the Weser in Bad Karlshafen.