Schmallenberg (German pronunciation: [ˈʃmalənbɛʁk] ^ⓘ; Westphalian: Smalmereg) is a town and a climatic health resort in the High Sauerland District, Germany. By area, it is the third biggest of all cities and towns of the state of North Rhine-Westphalia and the second biggest of the region of Westphalia.

With small Schmallenberg central town and the rural Bad Fredeburg Kneipp health resort the town has two urban settlements. Additionally, 82 villages and hamlets belong to the town's territory. Also being called “the Schmallenberg Sauerland”, the Town of Schmallenberg is famous for its total of five health resorts and nine villages which have been awarded gold for their beauty in the nationwide “Our village has a future [de]” contest.

Schmallenberg is located in the southeast of the Sauerland mountainous landscape. The Rothaar Mountains make up a part of the town's territory. Through the central town flows the river Lenne.

It is situated (linear distances):

Schmallenberg in the north borders on the Municipality of Bestwig and the Town of Meschede, in the east on the Town of Winterberg, in the south on the Town of Bad Berleburg, and in the west on the Municipality of Eslohe (Sauerland) and the Town of Lennestadt.

In the 1975 local government reorganization in the Sauerland and Paderborn the already existing Town of Schmallenberg was merged with the Town of Fredeburg (“Bad Fredeburg” today) and with the Municipalities of Berghausen, Bödefeld-Land, Dorlar, Fleckenberg, Freiheit Bödefeld, Grafschaft, Lenne, Oberkirchen, Rarbach and Wormbach which consisted of a total of 82 villages and hamlets.

On December 31, 2019 the modern Town of Schmallenberg had 25,146 inhabitants by main residence in the following 83 places:

Schmallenberg twin towns are: