A DOI, or Digital Object Identifier, is a string of numbers, letters and symbols used to permanently identify an article or document and link to it on the web. The DOI system provides a technical and social infrastructure for the registration and use of persistent interoperable identifiers, called DOIs, for use on digital. A digital object identifier is a persistent identifier or handle used to identify objects uniquely, standardized by the International Organization for Standardization. A digital object identifier (DOI) is a persistent identifier or handle used to identify objects. A DOI (Digital Object Identifier) is a standardized unique number given to many ( but not all) articles, papers, & books, by some publishers,.