Numedal is a traditional district and valley Buskerud, Norway. Running north–south, it extends between Kongsberg in the south to Rødberg in the north, passing through the municipalities of Kongsberg, Flesberg, Rollag and Nore og Uvdal.. The river Numedalslågen, the third-longest in the country, flows through the valley before discharging into Oslofjord at Larvik. As of 1 July 2004 the population of Numedal was 6,631, but the population has been consistently decreasing. The Numedal Line runs through the valley, as does National Road 40.
The Norse form of the name was Naumudalr. The first element is the genitive of the rivername Nauma f (now Numedalslågen), the last element is dalr m 'dale, valley. The name, and the meaning, is identical with Namdalen.
The area along the Numedalslågen from Kongsberg up to the Hardangervidda through the valley had the highest concentration of medieval log buildings. Numedal has long been the location of the Norwegian paths (Nordmannsslepene) which were the main traffic artery between Østlandet and Vestlandet. The path is marked, and when one treks along the old way, one sees the remains of Stone Age dwelling places, bog iron works, grave mounds and many more signs of activity over a period of 8000 years. There are still over 40 ancient timber buildings and 4 stave churches remaining.