You may need to include a DOI for some citation styles. Both Chicago/Turabian and APA say you should use a DOI instead of a URL for digital sources.

When should I look for a DOI?

DOI stands for digital object identifier. The idea is that the DOI provides a single, unique identifier that can always be used to track down the source -- even when formats and platforms change. 

  • DOIs are most commonly associated with articles, but other types of sources also have DOIs.
  • DOIs are not issued automatically; they must be registered with the DOI System by the responsible agency (usually the publisher);
  • Books usually only have DOIs when there is an online version.  However, a publisher may request a DOI if there is important information about the book available online.
  • The DOI system dates back to 2000. However, some materials published prior to 2000 have had DOIs applied to them retrospectively.
  • DOIs are standard, so there will not be more than one for any article or book.
  • If an article/chapter from a book is available separately online, or if it appeared in another source (such as a journal) prior to being included in the book, then it might have a DOI.

How do I find the DOI?

  1. The DOI will usually be printed somewhere on the first page of the article.  Look at your copy or scan - you may have to hunt.
  2. If you are using a database like PsycInfo or Web of Science, the DOI will be included (if it exists) in the database record.

Web of Science screenshot with a red arrow pointing to the DOI field under the article title


  1. Many library databases include tools that will generate citations for you.  Look for a "citation" or "cite" link or create a citation to see if it includes a DOI.

Screenshot from PsycArticles with the citation link underneath the journal cover image opened and a red arrow pointing to the DOI at the end of the citation

  1. The CrossRef service,  offers a  free DOI look-up “guest” form for determining if an article has a DOI. This may be useful when a DOI was not included in the citation.