OPUS is an open-source software package under the GNU General Public License used for creating Open Access repositories that are compliant with the Open Archives Initiative Protocol for Metadata Harvesting.

It provides tools for creating collections of digital resources, as well as for their storage and dissemination.

OPUS, originally an acronym for the Online Publikationsverbund der Universität Stuttgart, was developed with the support of the Deutsches Forschungsnetz (DFN) in 1997 and 1998 at the University of Stuttgart Library.

[2] The Library Service Centre for Baden-Württemberg [Wikidata] (BSZ) took over development from University of Stuttgart Library, however, since December 2010, the Cooperative Library Network of Berlin-Brandenburg [Wikidata] (KOBV) has taken over the development and management of the project at the Zuse Institute Berlin (ZIB).

[5] The current version, OPUS 4, is being developed by the Cooperative Library Network Berlin-Brandenburg (KOBV) at the Zuse Institute Berlin (ZIB).