What Is a DOI and How to Use It in Citations

A DOI (Digital Object Identifier) is a permanent link to a digital document. Think of it as an ISBN for online content -- it never changes, even if the URL does. Most citation styles now require a DOI when one's available.

What Does a DOI Look Like?

A DOI is a string that starts with 10. followed by a prefix (identifying the publisher) and a suffix (identifying the document):

10.1038/nature12373

When formatted as a URL (which most styles now require):

https://doi.org/10.1038/nature12373

Every DOI resolves to the current location of the document. Even if a journal changes its website, the DOI link still works.

How to Find a DOI

On the Article Page

Most journal articles display the DOI on the first page, usually near the title, abstract, or footer. Look for "DOI:" or "https://doi.org/" followed by a string.

In the Database

If you found the article through Google Scholar, PubMed, or a library database, the DOI is usually listed in the article metadata. If you have a PubMed ID instead, you can generate a citation directly from the PMID.

Using CrossRef

If you can't find a DOI, search for the article on CrossRef. Enter the title, and CrossRef will return the DOI if one exists.

Not Everything Has a DOI

DOIs are standard for journal articles, conference papers, and some books. They're less common for:

• Websites and blog posts
• Government reports
• Older publications (pre-2000)
• Theses and dissertations (some have DOIs, many don't)

If no DOI exists, use the URL instead. Don't make one up or leave the field blank.

DOI Format by Citation Style

APA 7th Edition

Format the DOI as a full URL. No "Retrieved from" prefix. No period at the end.

Smith, J. D. (2025). Article title. Journal Name, 15(3), 45--62. https://doi.org/10.1234/example

MLA 9th Edition

MLA includes the DOI as a URL, prefixed with doi.org/:

Smith, John D. "Article Title." Journal Name, vol. 15, no. 3, 2025, pp. 45--62, doi.org/10.1234/example.

Chicago 17th Edition

Chicago uses the full DOI URL:

Smith, John D. "Article Title." Journal Name 15, no. 3 (2025): 45--62. https://doi.org/10.1234/example.

IEEE

IEEE places the DOI at the end after "doi:":

J. D. Smith, "Article title," Journal Name, vol. 15, no. 3, pp. 45--62, 2025, doi: 10.1234/example.

For a full comparison of how these styles differ, see our citation style comparison.

Common Mistakes

1. Using the old dx.doi.org format -- The current standard is doi.org (without dx.)
2. Adding "Retrieved from" before the DOI -- Not needed in APA 7th edition
3. Putting a period after the DOI URL -- This can break the link
4. Using the DOI number without the URL prefix -- Most styles now want the full https://doi.org/ URL
5. Omitting the DOI when it exists -- Always include it if available

Try It with CiteTools

The fastest way to get a perfect citation from a DOI: paste it directly into CiteTools.io. We'll look up all the metadata automatically and format the citation in your chosen style. Just paste 10.1038/nature12373 or https://doi.org/10.1038/nature12373 -- both work.