The Open Metadata Registry (formerly the NSDL Registry) is a fundamental piece of technical infrastructure for the Semantic Web. While originally built to support the National Science Digital Library (NSDL), the Registry is available openly and to all who wish to use its services. The Registry software builds on open source technologies and is available as open source software under a GNU Affero General Public License.

The Registry provides a means to identify, declare and publish through registration metadata schemas (element/property sets), schemes (controlled vocabularies) and (soon) Application Profiles (ontologies). In addition to supporting registration of schemes, schemas and profiles for consumption and use by human and machine agents, the Registry intends to support the machine mapping of relationships among terms and concepts in those schemes (semantic mappings) and schemas (crosswalks). Thus, the Registry intends to support the key goals of metadata discovery, reuse, standardization and interoperability locally and globally with native support for RDF, SKOS and XML/RDF interoperability.

The Registry used as its inspiration the open-source Dublin Core Metadata Initiative (DCMI) Registry. The Registry extended the original DCMI goals to support: (1) the automated creation and maintenance of schemas and application profiles; and (2) the submission of schemas and schemes to a registry workflow for review and publication. All of the development work leverages the latest knowledge and standards for networked knowledge organization systems, schema and application profile declaration, and registry development.

The Open Metadata Registry project was funded by the National Science Foundation for its first three years.