According to the APA style guide to electronic references ( , 366k), writers must include an article's  DOI (Digital Object Identifier) in citations if there is one for that article.

Below is a brief guide to finding an article's DOI. More information on what DOI's are is available as well as all the changes to APA style as of July 2007.

There are three places where you can find the DOI.

1. From the article page in a database.

2. From the article page in a journal.

3. From the first page of an article.