This commemorative publication for Johannes Seidl, depicts the wide ranged work of a scientist who, through his professional, academic, journalistic and organizational life's work, has four extensive historical subject areas, namely Archive History and Collection, Medieval Studies, the University History and the History of Science (particularly natural science). The celebratee often succeeded in skilfully linking these different research areas, whereby often the biography served as a bond. The geologists Eduard Suess and Ami Boué in particular have long been companions in his scientific oeuvre.