Warstein ([ˈvaːɐ̯ˌʃtaɪn] ⓘ) is a municipality with town status in the district of Soest, in North Rhine-Westphalia, Germany.

Warstein is located north of the Arnsberger Wald (forest), at a brook called Wäster.

While named for the main settled portion within its 157.91 square kilometres (60.97 sq mi) total area, the town can be roughly divided into the following subdivisions (German: Ortsteil): The evidence of human life was found in the Bilstein Cave [de] between Warstein and Hirschberg.

Historians once thought Warstein was organized as an official town in 1276, but its exact charter date is unclear.

In addition to its mills, the overall Siepmann Group head office is located in Warstein.