The Ardennes is a region of extensive forests, rolling hills and ridges formed within the Givetian (Devonian) Ardennes mountain range, primarily in Belgium and Luxembourg, but stretching into France (lending its name to the Ardennes département and the Champagne-Ardenne région), and geologically into the Eifel. In Wallonia, the word 'Ardenne' in the singular is commonly used for the Belgian part of the region and in the plural for the French one.
Ardenne is the origin of the great industrial period of Wallonia, the second of the World (18th, 19th and 20th centuries). In France, the word 'Ardennes' in the plural, together with the definite article, is commonly used to refer to the French Department of that name. The Eifel range in Germany adjoins the Ardennes and is part of the same geological formation, although they are conventionally regarded as being two distinct areas.