The Rothaar Mountains (German: Rothaargebirge, also Rotlagergebirge), or Rothaar, is a low mountain range reaching heights of up to 843.1 m in North Rhine-Westphalia and Hesse, Germany.
It is believed that its name must once have been Rod-Hard-Gebirge, or "the cleared forest mountain range", as the range has nothing whatsoever to do with the colour red (rot in German), nor with hair (Haar).
The thickly wooded Rothaar, rich in mineral deposits, is found mostly in Westphalia between the Sauerland in the north, the Upland (northeastern foothills of the Rothaar) in the northeast, Wittgenstein Land in the southeast and the Siegerland in the southwest; only the range's southeastern foothills are actually in Hesse. It stretches from the upper Eder and the Lenne from the Kahler Asten (841 m) southwest of the Winterberg Tableland (Winterberger Hochfläche) some 30 km to the southwest and drops off steeply towards the west, but much less sharply towards the east.
The Rothaar is a narrow, banklike, mostly over 600 m high mountain chain forming geologically a large northeastern part of the Rhine Massif (Rheinisches Schiefergebirge). Since the land's elevation averages quite high, the mountains themselves, up to the 843.1 m-high Langenberg hardly stand out from each other.
The Rothaar Mountains are more or less co-extensive with the Rothaar Mountain Nature Park, parts of which do, however, reach into neighbouring geological areas, such as the ones named here.
In the northern Rothaar rise, among others, the rivers Diemel, Lenne, Neger, Nuhne, Odeborn, Orke, Ruhr, Wenne and Wilde Aa. In the south rise the Dill, Eder, Ferndorfbach, Ilse, Lahn and Sieg. Over the range runs the Rhine-Weser watershed. In the farthest southwest of the Rothaar are the Obernau and Breitenbach dams.