A DOI, or Digital Object Identifier, is a unique alphanumeric string assigned to online articles, books, and other works. It is a standardized unique number given to many articles, papers, and books by some publishers to identify a particular publication. DOIs make it easier to retrieve works, which is why citation styles like APA and MLA recommend including them in citations. A DOI is a permanent ID that, when appended to http://dx.doi.org/ in the address bar of an Internet browser, will lead to the source. The publisher assigns a DOI when the article is published and made available electronically. DOIs are important in academic citation because they are more permanent than URLs, ensuring that your reader can reliably locate the source. A DOI will help your reader easily locate a document from your citation, and it is more reliable and permanent than a URL.