CrossrefCrossref operates one of the largest DOI registration services in the world, and the Crossref Metadata Schema is the XML vocabulary through which publishers deposit bibliographic metadata about their scholarly outputs. With over 23,000 members from 164 countries and more than 150 million metadata records, the schema underpins the persistent citation linking infrastructure that connects the scholarly communication ecosystem.
Background
Crossref was launched in early 2000 as a cooperative effort among publishers to enable persistent cross-platform citation linking in online academic journals. The organization functions as the largest DOI Registration Agency under the International DOI Foundation. The metadata schema evolved alongside the service, growing from a simple journal article deposit format into a comprehensive XML schema covering multiple content types.
The schema is maintained by Crossref and developed through consultation with its membership, which includes publishers, libraries, research institutions, and funders. The metadata deposited through the schema is made openly available under a CC0 waiver, supporting reuse without restriction.
Purpose and Scope
The Crossref Metadata Schema defines the XML structures that publishers use to register DOIs and deposit associated bibliographic metadata. It covers a wide range of scholarly content types:
- Journal articles -- the original and still most common use case
- Books and book chapters -- including monographs, edited volumes, and reference works
- Conference proceedings -- papers presented at scholarly conferences
- Datasets -- research data associated with publications
- Preprints -- posted content prior to peer review
- Grants -- research funding awards (via the Open Funder Registry)
- Peer reviews -- review reports linked to the reviewed work
- Standards and reports -- technical reports and standards documents
Key Metadata Elements
The schema captures a rich set of metadata elements for each deposited item, including:
| Element | Description |
|---|---|
| Title | Title of the work |
| Contributors | Authors and other contributors, with ORCID iDs |
| Publication date | Date of publication |
| DOI | The assigned persistent identifier |
| ISSN/ISBN | Standard serial or book identifiers |
| Abstract | Text of the article abstract |
| References | Cited references enabling citation linking |
| Funding | Funder names and award numbers |
| License | Access and reuse license information |
| Crossmark | Update, correction, and retraction metadata |
Serializations and Technical Formats
The schema is defined in XML Schema (XSD) format. Metadata is deposited via XML, and the Crossref REST API returns metadata in JSON. The schema library documents multiple schema versions for different content types, with the overarching deposit schema at version 5.4.0.
Governance and Maintenance
Crossref is a nonprofit association (501(c)(6)) headquartered in Lynnfield, Massachusetts. The schema is developed and maintained by Crossref staff in collaboration with the member community. Changes to the schema are documented in the schema library, with versioned XSD files for each content type. The sustainability model includes annual membership fees, per-record registration fees, and additional service fees.
Notable Implementations
Crossref metadata is central to the scholarly communication infrastructure:
- All major academic publishers (Elsevier, Springer Nature, Wiley, Taylor & Francis, etc.) deposit metadata via the schema
- The Crossref REST API serves over 1 billion metadata queries per month
- OpenAlex, Semantic Scholar, Google Scholar, and other discovery services consume Crossref metadata
- Reference linking services use Crossref metadata to resolve billions of DOI links monthly
- The Retraction Watch database was acquired by Crossref and integrated into the metadata infrastructure
Related Standards
- DataCite Metadata Schema -- a parallel DOI registration schema for research data, with metadata exchange coordination between the two organizations
- ORCID -- researcher identifiers integrated into Crossref contributor metadata
- Open Funder Registry -- controlled vocabulary of funding organizations used in Crossref grant metadata