This paper presents a taxonomy for open hypermedia systems. The purpose of the Flag1 taxonomy is manifold: 1 to provide a framework to classify and concisely describe individual systems, 2 to characterize what an open hypermedia system is, 3 to provide a framework for comparing di erent systems in a system independent way, and 4 to provide an overview of the design space of open hypermedia systems. The Flag taxonomy builds on the achievements of the Dexter model. It extends the terminology of the Dexter model to adequately cover issues that relate to open hypermedia systems such as integrationand use of thirdparty applications to edit and display hypermedia components. Two of the most prominent open hypermedia systems, DeVise Hypermedia and Microcosm, are used as case studies. The Flag taxonomy is used to compare these systems on a carefully selected set of aspects that distinguish open hypermedia systems from other hypermedia systems.