What is a DOI? Understanding Digital Object Identifiers

A DOI (Digital Object Identifier) is a unique, permanent alphanumeric string assigned to a digital document — typically a journal article, book chapter, or dataset. It serves as a persistent link to the content, meaning that even if the publisher changes their website URL, the DOI will always resolve to the correct location of the document.

DOIs are managed by the International DOI Foundation and assigned by registration agencies such as CrossRef (for academic publications) and DataCite (for research datasets). A DOI looks like this: 10.1000/xyz123. The "10" prefix identifies it as a DOI, the number before the slash identifies the publisher or registrant, and the string after the slash is the unique identifier for the specific document.

10.1038/s41586-020-2649-2

As a URL: https://doi.org/10.1038/s41586-020-2649-2

DOIs solve a fundamental problem in academic referencing: link rot. Studies have found that up to 20% of URLs in published papers become broken within a few years as websites are restructured, articles are moved, or publishers change their platforms. A DOI never breaks because it is a redirect — when you follow a DOI link, it is resolved through the doi.org system to the current location of the document.

Including a DOI in your citation gives your reader a reliable, one-click path to the source. It also helps citation databases like Google Scholar, Scopus, and Web of Science match your references to the correct publications, which improves the accuracy of citation counts and scholarly metrics.

The DOI is usually printed on the first page of a journal article, near the title or in the footer. In online versions, it often appears as a clickable link near the article metadata. If you cannot find a DOI on the document itself, you can search for it using these tools:

• CrossRef DOI lookup (doi.crossref.org) — search by title, author, or bibliographic details
• DOI.org — enter a DOI to verify it resolves correctly
• Google Scholar — click the article title, then look for the DOI in the article metadata
• CiteMe — paste an article title or search by keyword; if a DOI exists, CiteMe will include it automatically

Not every publication has a DOI. Books, older journal articles, conference papers, and reports may not have been assigned one. In these cases, use the URL of the source or omit the locator field, depending on what your citation style requires.

Each citation style has specific rules for how DOIs should appear in your reference list. The most common difference is whether the DOI is presented as a URL (starting with https://doi.org/) or as a plain identifier (starting with doi:). APA 7th edition standardised on the URL format, and most other styles have followed suit.

Walker, M. (2017). Why we sleep. Scribner. https://doi.org/10.1234/example

Walker, Matthew. Why We Sleep. Scribner, 2017. https://doi.org/10.1234/example.

Walker, Matthew. 2017. Why We Sleep. Scribner. https://doi.org/10.1234/example.

Walker M. Why we sleep. Scribner; 2017. doi:10.1234/example

Notice that APA, MLA, and Chicago now use the full https://doi.org/ URL format, while Vancouver still uses the "doi:" prefix without "https://". Always check your style guide for the current requirements, as DOI formatting rules have changed across recent editions.

Students frequently make small errors with DOIs that can affect the usability of their references. Here are the most common mistakes and how to avoid them:

• Using "doi:" instead of "https://doi.org/" in APA 7 — the older "doi:" prefix was used in APA 6, but APA 7 requires the full URL format
• Adding a period after the DOI — APA and MLA do not place a period at the end of a DOI URL because it could break the link
• Using a database URL instead of the DOI — always use the DOI when available, not the library database link (e.g., not the EBSCOhost or JSTOR URL)
• Hyperlinking only part of the DOI — make sure the entire DOI string is included in the hyperlink, including any special characters
• Omitting the DOI entirely — if a DOI exists for your source, leaving it out makes it harder for readers to locate the document