Q. What is a DOI?

DOI stands for "digital object identifier."

A DOI is an alphanumeric string (meaning that it may contain letters and/or numbers) that is used to uniquely identify an online journal article or book, etc. All DOIs contain 10. followed by four numbers and then a forward slash and then a string of letters and/or numbers -- for example: 10.1093/jopart/muq015

You will sometimes see an article's or a book's DOI in its record in a database or on its PDF.

Note, though, that not all online articles or books have a DOI, since it's optional for publishers to assign a DOI to an online source.

If you are citing an online journal article using APA style, the article's DOI should be the last element of your citation. For more information about citing an article with a DOI, please see the library's APA citation examples for academic journal articles.

The APA citation examples page noted above also gives instructions for citing an online journal article that doesn't have a DOI.

For more about DOIs, see Information About DOIs.