A DOI or digital object identifier is a unique identifier assigned to a scholarly piece of work, such as a journal article. Its purpose is to help with location, identification and attribution.
APA referencing requires you to include a DOI in your reference list (if one is available). Sometimes, the DOI is difficult to locate or there simply isn't one. If you have checked the tools listed below and still can't find one, follow the directions in the Citing and referencing guide for examples.