What is a DOI?

A DOI is a digital object identifier, a unique number that is assigned to a digital or electronic work.  A DOI that is assigned to a scholarly article basically works the same way an ISBN number works for a print book. It is a unique identifier for that article. The DOI also allows for a permanent link to be made to the electronic version of that article, whereas URLs may expire or move.  Electronic books may also be assigned DOIs.

Here is the explanation of the DOI system from the International DOI Foundation (IDF), from http://www.doi.org/:

The Digital Object Identifier (DOI®) System is for identifying content objects in the digital environment. DOI® names are assigned to any entity for use on digital networks. They are used to provide current information, including where they (or information about them) can be found on the Internet. Information about a digital object may change over time, including where to find it, but its DOI name will not change.
The DOI System provides a framework for persistent identification, managing intellectual content, managing metadata, linking customers with content suppliers, facilitating electronic commerce, and enabling automated management of media. DOI names can be used for any form of management of any data, whether commercial or non-commercial. The DOI System is an ISO International Standard.

Where can I find the DOI?

Newer journal articles will often include the DOI on the title page:



For articles found by searching a subject database, check the full article record for the DOI.



Additionally, you can use the free DOI lookup tool from Crossref.org. Use the article's title and other identifying information to search for the DOI.


How do I include the DOI in my citation?

APA Style

The 6th edition of APA style requires the inclusion of the DOI in all citations to electronic journals.  Even if you have read an article in print that includes a DOI, it is still necessary to include that DOI in your citation.  Here is an example citation including the DOI:


For more information on DOIs and APA style, see A DOI Primer, by Chelsea Lee, as posted on the APA Style Blog.

Chicago Manual of Style

When documenting your sources using the Chicago Manual of Style, always provide the DOI when it is available.  See section 14.6 for more information on DOIs.  Example bibliography entry:

Novak, William J. “The Myth of the ‘Weak’ American State.” American Historical Review 113 (June 2008): 752–72. doi:10.1086/ahr.113.3.752.

CSE (Council of Science Editors)

CSE also requires online article citations to include the URL and DOI, where available.  See the CSE Quick Citation Guide from the Pennsylvania State University Libraries for more information and example citations.

Other Citation Styles

Always consult with the official style guide for the style you are using to write your paper.  See our Citing & Evaluating Research guide for more information.

How do I use a DOI?

As a writer, you may feel that searching out DOIs for your citations is a cumbersome process.  DOIs are meant to assist your reader, so take advantage of the convenience of DOIs when you are doing your research.  DOIs can make it much easier to find the full text of an article.

For example, you can enter a DOI into the library's Articles & More search to instantly search Falvey's full text holdings.

Even more convenient, you may find that some newer PDF versions of articles automatically hyperlink the DOI to the referenced article.  Simply click the DOI to access the full text of the referenced article.  (Off-campus users may need to authenticate as members of the Villanova community before accessing subscription materials.)

More broadly, you can simply enter the DOI into the  DOI Resolver from crossref.org. The same task can be accomplished by pasting the URL http://dx.doi.org/ immediately followed by the DOI into your address bar and then clicking enter.