Answered By: APUS Librarians
Last Updated: Jan 27, 2021     Views: 36722

A DOI (Digital Object Identifier) is a standardized unique number given to many (but not all) articles, papers, & books, by some publishers, to identify a particular publication. 

To find a DOI number for an article, look on the first page and in the header or footer information.  If you see a "DOI:" followed by a string of numbers, you'll know that you have found it. 

If you have a reference and can't find the DOI number, or have a DOI number and are missing the reference, click here to search Crossref

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Example of an article DOI

To use a DOI in a citation:

All the style guides used by APUS state that, when citing electronic sources, one should use the most stable link available. If you cannot locate a DOI for a source you want to cite -- simply leave it out.

  • APA: APA citation style calls for the inclusion of DOI numbers in a citation - when available. Read more here.
  • Bluebook: The Bluebook editors have no designated preference re: DOIs. They do state that “All efforts should be made to cite the most stable electronic location available,” (Section 18.2.2 Subscription resource.  Please log in with your student id and password.) but this may or may not be a DOI.
  • Chicago: The CMS editors say “A DOI, if it is available, is preferable to a URL.” (Section 14.184 Subscription resource.  Please log in with your student id and password.)
  • MLA: The MLA Handbook says: “When possible, citing a DOI is preferable to citing a URL.” (48). Read more here.
  • Turabian: The editors of Turabian state “If a website gives a preferred form of the URL, along with the citation for a source, use that rather than the URL in your browser’s address bar. Some sources are identified by a DOI (digital object identifier). URLs based on DOIs are more persistent and stable that URLs. To cite a source that includes a DOI, append the DOI to in your citation.” (Section


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