GUIDES · DOIS
What is a DOI?
A DOI, or Digital Object Identifier, is a permanent ID for a published work: a journal article, a book or chapter, a dataset, a piece of software. Unlike a web address, it is meant to keep pointing to the work when the publisher moves its website, which is why citation styles ask for it.
How a DOI is built
Every DOI starts with 10., then a prefix that identifies the organization that registered it, a slash, and a suffix that organization chose for the work:
| Part | Example | What it means |
|---|---|---|
| Prefix | 10.1038 | The registrant, here the publisher of Nature |
| Suffix | nature14539 | The work itself, chosen by the registrant |
| Whole DOI | 10.1038/nature14539 | LeCun, Bengio and Hinton’s 2015 review “Deep learning” |
DOIs are not case-sensitive, and the suffix can contain almost any character, including parentheses and angle brackets in some older ones. The system is run by the DOI Foundation and standardized as ISO 26324. Registration agencies issue DOIs: Crossref for most journals and books, DataCite for most datasets, software and repositories, and a few others.
Opening a DOI
Put https://doi.org/ in front of a DOI and it becomes a link to the work’s current page: https://doi.org/10.1038/nature14539. When a publisher moves an article, it updates the DOI’s record to point to the new page. Keeping the DOI record updated lets the same link survive a move. Outdated records and service outages can still prevent it from opening. Older links written as http://dx.doi.org/ still work, but https://doi.org/ is the current form.
How to find a DOI
- Look at the work. Most articles print the DOI on the first page, near the title or in the header or footer, and on the publisher’s page for the article.
- Search by title. Crossref’s search finds Crossref DOIs from a title or a full reference, and the citation generator on this site can search by title too, then format the citation for you.
- Check the database you found it in. Library databases, Google Scholar records and preprint servers usually show a DOI when the work has one.
DOIs in citations
APA 7 and MLA 9 both ask you to give a DOI, when a work has one, as a full https://doi.org/ link at the end of the reference:
LeCun, Y., Bengio, Y., & Hinton, G. (2015). Deep learning. Nature, 521(7553), 436–444. https://doi.org/10.1038/nature14539
A DOI also lets a tool fill in the rest of the reference: paste one into the free citation generator to get the citation in APA, MLA, Chicago, IEEE and ten more styles, or as BibTeX for LaTeX. Always check the result against the work itself, because a registry’s record can be incomplete.
When a work has no DOI
Many books, older articles, reports and web pages have none. Cite them with the details your style asks for, and a stable URL where there is one. Don’t invent a DOI or use one that belongs to a different version of the work, such as a journal’s DOI for a preprint you actually read.
Docr’d, which makes this page, is a research library in early access that looks up DOIs for the papers you add and keeps their citations ready in 14 styles.