Answer
A DOI, or Digital Object Identifier, is a unique string of numbers and characters that are assigned to an online source including books and journal articles. A DOI acts as a permanent, stable link to a source and is often included as part of a citation in MLA, APA, and Chicago.
For most scholarly journal articles the DOI will be included in the database record and when opening the full text of the article. Common locations within an article to find the DOI include near the title, or in the header or footer on the first page.
