The article explores the object and the methodology of conceptual history, by elaborating on Reinhart Koselleck's idea of key concepts, and proposes to study them according to two different aspects of meaning: The representational aspect, which touches upon the relations between words and concepts and studies words and concepts within semantic fields, and the referential aspect, which brings in both the social history reflected in semantic changes and the contexts in which the concepts serve as factors, and which make the use of the concepts possible. The article concludes with a methodological suggestion for the use of digitized textual databases for diachronic as well as synchronic histories of concepts.