Digital Object Identifiers (DOIs) are special strings of alphanumeric characters that form a persistent, or permanent, link to individual publications. They are issued at the time of publication, much like an ISBN or a serial number. DOIs can be attached to a number of different publications, including journal articles, books and chapters, conference papers, and so on.
A number of referencing styles (including APA,and Chicago,) require that you include DOIs for publications where they have been assigned. This guarantees that others will be able to access your listed references, as DOIs offer persistence and permanence that standard URLs (links) do not.
Ref: Thank you to the University of Newcastle Library
