A digital object identifier (DOI) is a unique alphanumeric string assigned by a registration agency (the International DOI Foundation) to identify content and provide a persistent link to its location on the Web. The publisher assigns a DOI when an article is published and made available electronically. The DOI is unique to an individual work. Not all publishers participate in the DOI initiative; therefore, an article may or may not have a DOI assigned.
All DOI numbers begin with a 10 and contain a prefix and a suffix separated by a slash. The prefix is a unique number of four or more digits assigned to organizations; the suffix is assigned by the publisher and was designed to be flexible with publisher identification standards.