While the study of medieval charters has an ample tradition in the big field of auxiliary sciences of history, the illumination contained in some of these sources has often been neglected. Also art-historians normally didn't take notice of the often prestigious combination of legal sources and artistic decoration. The present paper offers an interdisciplinary view on this widely ignored field of research and tries to distinguish between three large groups of illuminated charters that differ in their functions. Firstly, decorated charters – which are usually quite impressive due to their colorfulness and size – may contribute to the shaping of identity of a group of persons. Secondly, they can also serve as show pieces with the foremost aim of attracting the attention of beholders. Finally, the decoration can also help to increase the appeal and the value of the charter. The interdisciplinary project Illuminated Charters as "Gesamtkunstwerk", funded by the Austrian Science Fund FWF (P26706-G21) and based in both Vienna and Graz, deals extensively with all three aforesaid types of illuminated charters and aims at providing an open access database within the framework of the virtual document archive monasterium.net, where several hundred charters should be introduced by way of a fully structured diplomatic and art historical description.