What Is a DOI?
A DOI, or digital object identifier, is a unique and permanent code that identifies an article, book chapter, dataset or other digital item. It is designed to keep pointing to the item even if the web address changes, so that readers and citation systems can reliably find it. DOIs are used by most scholarly journals and many publishers.
What a DOI looks like
A DOI has a prefix and a suffix separated by a slash, for example 10.1234/abcd.5678. The prefix identifies the publisher or organization, and the suffix identifies the item. When used as a link, it follows the resolver address, so that the link looks like https://doi.org/10.1234/abcd.5678. Clicking it takes you to the current location of the item.
Why DOIs matter
- Permanence: ordinary URLs break when sites reorganize, while DOIs are maintained.
- Accurate citing: a DOI points to the exact item, which reduces confusion between similar titles.
- Tracking: databases and metrics services use DOIs to link citations to articles.
- Finding versions: tools can use DOIs to find open-access copies.
Using DOIs in citations
Most major citation styles ask you to include a DOI when one exists. For example, APA 7 asks for the DOI formatted as a link at the end of the reference. MLA, Chicago and Harvard variants have similar practices, with details differing. Check your style guide, and copy the DOI carefully, since a single character wrong breaks the link.
How to find one
- Look on the article itself, near the title, abstract or footer.
- Check the database record or publisher page.
- Use a DOI lookup tool, such as one provided by the main registration agency, to search by title and author.
- Use your reference manager, which can fetch records from a DOI or title.
Checking that it works
Test the link by pasting it into a browser. If it does not work, compare it with the original. For research integrity, do not cite an article you cannot find. A DOI that does not resolve may indicate a typo or a fabricated reference.
Other identifiers
You may also see ISBNs for books, ISSNs for journals, PubMed IDs and arXiv IDs. They serve similar purposes in different systems.
Related terms
See citation style, bibliography, scholarly journal, preprint and open access.
Frequently asked questions
Where can I find a DOI?
On the first page of a journal article, on the publisher's web page, in library database records and in the reference list of other papers. You can also search a DOI lookup service by title.
How do I turn a DOI into a link?
Add the resolver address before it, so that a DOI like 10.1000/example becomes https://doi.org/10.1000/example. Many styles now ask you to format DOIs this way.
What if a source has no DOI?
Not all do, especially older articles and some books. Cite using the other details your style requires, such as a stable URL, if appropriate.