Q. How do I find the DOI of an article I'm citing?

The digital object identifier (DOI) is a unique number assigned to an article.  Not all articles, especially articles before 2002 or so, will have a DOI assigned to them.  If you do see that an article you are citing has a DOI, APA citation style recommends that it be included in the citation.

If a DOI has been assigned to an article, one place to check is the first page of the article itself (usually with the letter DOI or doi in front of the number).  Another place to check for a DOI is by reviewing the citation record of the article in the research database where the article was found.

In addition, you may wish to search for your article in Crossref to see if it has been assigned a DOI.