The main objective of the Open Encyclopedia System project, funded by the German Research Foundation (DFG), is to develop a standardized, open source online platform for building and maintaining online encyclopedias in the humanities and social sciences that provide readers worldwide free and unrestricted online access to open access scientific content. The project consortium is made up of four partners: the Center for Digital Systems (CeDiS), the Friedrich-Meinecke-Institut – Department of Modern History (FMI), the Center for Modern Greece (CeMoG), and the Bavarian State Library (BSB) in Munich. Based on the experience gained in building an online encyclopedia on the First World War “1914-1918-Online,” we are developing a digital framework that hosts a collection of customizable workflow management and editing tools to create, publish and maintain academic reference works for digital encyclopedias. The project Open Encyclopedia System (OES) started in 2016 and, by the end of the project in 2019, it will offer a generic modular open source software system with which editors and users will be able to build an online encyclopedia on their own. Our aim is to create a system for users in which collaboration is easy and web-based. The OES software should be customizable, flexible and adaptable to context applications as well as simple to operate. Ultimately, the OES software should set a standard for saving time and for being a sustainable framework for this type of publication.