A digital object identifiers (DOI) is a unique alphanumeric that identifies content and provides a persistent link to its location on the Internet. All DOI numbers begin with a 10 and contain a prefix and a suffix separated by a slash. The sixth edition of the APA manual recommends including DOIs, whenever available, at the end of citations.
The library has a tool to help you find the DOI of an article.
Example of an article citation with a DOI included at the end.
B. J., & Lawler-Sagarin, K. A. (2005). Critically evaluating competing theories: An exercise based on the Kitty Genovese murder. Teaching of Psychology, 32(3), 167–169. doi:10.1207/s15328023top3203_8