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Citing Sources

Guides & Sample Papers

The OWL at Purdue provides resources that may useful for writing projects & citation help.

Click here for a full-length self-paced online tutorial from the APA's website.

Publication Manual

Copies of the Publication Manual are found in the reference and check out collections of the Philadelphia Campus Library and the Newtown LRC.

What Are DOI Numbers?

DOI numbers (Digital Object Identifier numbers) are unique numbers assigned by the International DOI Foundation. DOI numbers should make it easy for the reader to retrieve information about and the text of a document.

The URL where you retrieved the item could change. Therefore, it is not a persistent link to the source. The DOI number is a unique identifier that will always be associated with that particular source regardless of where the source was retrieved today (website, Holy Family databases, PubMed, etc.) or where it may be available in the future.

DOI numbers serve as links to the article when entered into a DOI resolver. See Retrieving Sources by DOI Number for more information.

If your source includes a DOI number, you must include it at the end of your reference.

Where Do I Find the DOI Number?

  • DOI numbers may be available on print and electronic items. (Be sure to look for a DOI number for your print sources too.)
  • DOI numbers are usually located on the first page of an article. This example is from an article in .pdf format. 
  • DOI numbers may also be found on the database landing page (detailed citation and record page) for an article. (The DOI number is typically one of the last pieces of information listed. There may be a lot of information on this page, so be sure to scroll all the way to the label that indicates "digital object identifier").

DOI Numbers in Citations

NOTE: Crossref, which registers DOI numbers, has updated their guidelines to a new format. It is correct to use the old or new formats.

  • If it is available, include the DOI number at the end of your reference citation. The doi can be listed in the following formats:



  • Make sure you use the DOI exactly as listed on the article or source you are citing.
  • Copy and paste the DOI number whenever possible rather than typing it out.
  • If you're including the DOI number, no other retrieval information (such as a URL) is required. 
  • If no DOI is available, a URL may or may not be necessary. Be sure to use the pull-down menus on the left to choose the correct citation format.

Retrieving Sources by DOI Number

DOI numbers serve as links to source content. (The full text may be available for free or offered for purchase.) These DOI numbers help researchers to locate content quickly and efficiently. A researcher would then enter the DOI number into a DOI resolver in order to retrieve the item.

DOI Resolvers:

As a Holy Family student, you can access the full text of materials in a variety of ways. The DOI is important for proper citation, but you can use the research databases and journal locator to locate the full text of many materials. Ask a librarian for more help!

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