The main objective of the project „Open Encyclopedia System (OES)“ is to develop a standardized web-based open source platform for building and maintaining scientific online encyclopedias, which will be publicly available, free of charge on the internet and accessible worldwide. Its first use cases will be "1914-1918-online. International Encyclopedia of the First World War" and the CeMoG-Encyclopedia on German-Greek Entanglements. The project consortium is carried out of four partners: Center for Digital Systems (CeDiS), Friedrich-Meinecke-Institut (FMI), Center for Modern Greece (CeMoG) all based at the Freie Universität Berlin, as well as the Bavarian State Library (BSB) in Munich.