In recent decades there has been increased interest and fascination in the concept of openness as a kind of communication. Openness is in fact a communicative ideal of the modern age because this ideal has existed without interruption since the Enlightenment. Another reason is that the idealization of openness is closely interwoven with central social and intellectual developments that were intensified in the modern age. Based on a wide spectrum of sources concerning communication, Juliane Schröter examines the history of this ideal from the 18th century to the present.