The High Fens (French Hautes Fagnes, Dutch Hoge Venen) is a cross-border, shield-shaped arched plateau between Germany and Belgium with an area of over 600 km². 133 km² of this is in Germany. In Belgium, around 54 km² (5,368 ha) of the Venn area are state-owned as domanial nature reserves of the High Fens, after it grew by 500 hectares on Belgian territory in 2018.
Large areas are designed as raised bogs, from which the name is derived: Venn, Fenn (Dutch Veen) for bog. With 694 m O.P. the Botrange is both the highest point in the High Fens and the highest mountain in Belgium.
Geologically, the High Fens belongs to the left bank of the Rhenish Slate Mountains, as does the bordering Ardennes and the Eifel as well as the Hunsrück south of the Moselle. It is often not viewed as an independent natural area, but is assigned to the western part of the Eifel and the eastern part of the Ardennes.
The Belgian part of the High Fens has been on the Belgian tentative list of UNESCO World Heritage sites since 2008.