Rjukan Falls (English) or Rjukanfossen (Norwegian) is a waterfall in the western part of the Vestfjorddalen valley in Tinn Municipality in Telemark county, Norway. The 104-metre (341 ft) tall waterfall is located on the river Måna, about 5 kilometres (3.1 mi) to the west of the town of Rjukan.

Historically, the waterfall was a major tourist attraction, being one of the first floodlighted waterfalls by electricity produced by the same waterfall. In 1905, the waterfall and surrounding river were harnessed by the Vemork hydro-electrical power plant to produce power for the saltpetre production at a nearby Norsk Hydro factory.

The waterfall is named Rjukanfossen in Norwegian (Old Norse: Rjúkandi). The first element is derived from the present participle of the verb rjúka which means "to emit smoke" or "to emit vapor" (referring to all the froth from the waterfall).

The last element is a later addition to the name which comes from the Norwegian word fossen which means "the waterfall".

• List of waterfalls#Norway
• Rjukandefossen