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Citation Styles & Tools

A brief explanation of citation fundamentals and a guide to useful resources.

What is a DOI?

A DOI, or Digital Object Identifier, is a persistent identifier to uniquely identify various objects, standardized by the International Organization for Standardization. In other words, it's a unique string of letters and numbers used to identify an article or book, and it's more permanent and reliable than a URL.

Any digital object can be assigned a DOI number, including books, academic journal articles, research reports, data sets, conference proceedings, media, governmental reports, and code.

Who assigns a DOI?

DOIs are assigned, governed, and managed by the International DOI Foundation. There are numerous DOI Registration agencies under the International DOI Foundation that provide services and registration of DOI numbers. Different agencies focus on different types of content. For example, EIDR manages DOI registrations for video and media content, such as television or movies.

Crossref is one of the International DOI Foundation's registration agencies, and is responsible for assigning DOIs to scholarly research publications.

What does a DOI look like?

A DOI starts with the number 10, followed by a period. They can appear as an alphanumeric string of digits, or as a webpage URL.  Here are a few examples:

  • 10.1093/ajae/aaq063
  • 10.1371/journal.pgen.1001111


  • Not every article or resource has a DOI! Sometimes you won't be able to locate a DOI because the resource has not been assigned one.
  • DOIs have nothing to do with peer review; both peer-reviewed and non-peer-reviewed resources can have a DOI.

Where can I find a DOI?

For most scholarly journal articles, the DOI can be found within the article itself, usually somewhere on the first page (check right below the title, or in the header or footer of the first page).

Look at information about the article. Library databases include information about an article, so if an article has a DOI, it may be listed in the item's record page. If you can't find the DOI in the article itself, check around the item record page to see if the DOI is listed.

If you can't find the DOI in the article itself, you can check for an assigned DOI.  Follow these steps to locate a DOI using Crossref:

1. Go to the website.

2. Select the "Search metadata" tab at the top of the search box. homepage with the search metadata tab circled

3. Enter the title of the article you are searching for in the title, author, DOI, etc. box and press Enter to run your search.

4. In the results list, the DOI will be listed at the bottom of each entry. For the following example, the DOI is 10.4324/9781351231879-2.

Note: The actual DOI begins with 10. For APA 7 style citations, include "" in front of the number.

Crossref example search with DOI circled in red

If you don't see the article you're looking for in the search results, you can try:

  • Use the Year limiter in the left column to limit results to only the year the item was published.
  • Include the author's last name with your search. This might look like:
    • "Social Neuroscience of Subjective Well-Being and Life Satisfaction" AND daSilva

If you have tried all of the above steps to locate the DOI for the article you are looking for in Crossref, it is safe to assume that the article does not have a DOI.

When it comes to citations, if you cannot find a DOI, use the resource's persistent URL instead.