Against the background of modern terminology theory (e.g. Picht 1993), this paper examines the concept of vagueness as it relates to legal concepts. It is often assumed in lay circles that, generally, legal concepts are or must be clear (and unambiguous). Legal experts (e.g. Heck 1932, Zingel 2001) claim on the contrary that many legal concepts are vague and only shed this inherent property after interpretation. The paper presents some empirical evidence in support of the view that many legal concepts are inherently vague.