Digital Object Identifier (DOI)
A DOI is a persistent identifier used to label digital objects such as journal articles, datasets, and software, so that they remain citable even when their location on the web changes. Maintained by the International DOI Foundation and assigned through registration agencies such as Crossref and DataCite, DOIs have become foundational infrastructure for scholarly communication.
A Digital Object Identifier (DOI) is a persistent identifier for a digital object, designed so that a reference to a paper, dataset, or piece of software keeps working even after the underlying file is moved or its host website changes. DOIs are standardised as ISO 26324 and have been governed by the International DOI Foundation (IDF) since 1998. A DOI is a string of the form `prefix/suffix`. The prefix always starts with `10.` followed by a number that identifies the registrant (for example `10.1126` for the publisher of Science), and the suffix is chosen by the registrant to identify a specific item. A real example is `10.1126/science.aaa1465`. Resolution happens through the Handle System: a user appends the DOI to `https://doi.org/`, and the resolver returns the current canonical URL for the object. If a journal migrates its archive or a publisher is acquired, the DOI keeps working as long as the registrant updates the target URL in the resolver. DOIs are issued through registration agency|registration agencies accredited by the IDF. Crossref is the largest, focused on scholarly publications such as journal articles, books, conference proceedings, and preprints, with more than 150 million records as of the mid-2020s. DataCite specialises in research data and other non-traditional outputs such as samples and models. mEDRA serves European publishers, and the Japan Link Center (JaLC), the Chinese agency ISTIC, and Airiti cover regional markets. Across all agencies the total number of registered DOIs is in the hundreds of millions and growing. The DOI ecosystem connects to neighbouring identifier systems. Crossref and DataCite both let registrants attach author ORCID iDs to deposited metadata, automatically updating a researcher's ORCID record when a new DOI naming them is registered. Software Heritage pairs its archival identifiers with DataCite DOIs so that specific snapshots of source code can be cited like papers. Funder information, grant IDs, and ROR affiliations are increasingly carried in the same metadata records. DOIs have well-known limits. Registration is not free: agencies charge membership and per-DOI fees, which can deter small publishers, individual authors, and many open community projects. Prefixes are tied to the registering organisation, so a journal that changes publishers may end up with two prefix histories rather than a clean lineage. DOIs can also go dead when a registrant stops maintaining target URLs or leaves the system, producing the same broken-link experience the standard was meant to prevent. Despite these caveats, the DOI has become the de facto persistent identifier of the scholarly record.