ISSNs are used in ordering, cataloging, interlibrary loans, and other practices in connection with serial literature.

[5] An ISSN is an eight-digit code, divided by a hyphen into two four-digit numbers.

The International Centre is an intergovernmental organization created in 1974 through an agreement between UNESCO and the French government.

ISSN-L is a unique identifier for all versions of the serial containing the same content across different media.

At the end of 2016,[update] the ISSN Register contained records for 1,943,572 items.

An ISSN, unlike the ISBN code, is an anonymous identifier associated with a serial title, containing no information as to the publisher or its location.

For this reason a new ISSN is assigned to a serial each time it undergoes a major title change.

Separate ISSNs are needed for serials in different media (except reproduction microforms).

However, the same ISSN can be used for different file formats (e.g. PDF and HTML) of the same online serial.

In the 1990s and onward, with personal computers, better screens, and the Web, it makes sense to consider only content, independent of media.

This "content-oriented identification" of serials was a repressed demand during a decade, but no ISSN update or initiative occurred.

A natural extension for ISSN, the unique-identification of the articles in the serials, was the main demand application.

An alternative serials' contents model arrived with the indecs Content Model and its application, the digital object identifier (DOI), an ISSN-independent initiative, consolidated in the 2000s.

The URNs are content-oriented, but ISSN is media-oriented: A unique URN for serials simplifies the search, recovery and delivery of data for various services including, in particular, search systems and knowledge databases.