Today, the demand for transparency is omnipresent. In particular, transparency is considered a prerequisite for good governance, for political participation and democracy. On closer inspection, however, transparency proves to be ambivalent. For complete transparency has not yet been achieved anywhere. Moreover, measures to increase transparency can have the opposite effect and stir up mis-trust. Historians are just beginning to discover this topic. The volume aims at elucidating the opportunities and the restrictions of transparency in historical research. It assembles contributions covering European history since the 19th century. The contributors focus on political and cultural history, but include also economic and media history as well as the history of ideas. They analyse publicly debated demands and efforts for transparency, conceived as the access to information or its disclosure.