An ISSN (International Standard Serial Number) is an 8-digit code used to identify newspapers, journals, magazines, and periodicals of all kinds and on all media, including print and electronic. It is an internationally recognized identification number for serial publications. The ISSN takes the form of the acronym ISSN followed by two groups of four digits, separated by a hyphen. The eighth digit is a check digit calculated according to a modulus 11 algorithm on the basis of the 7 preceding digits; this eighth control digit may be an “X” if the calculation results in a value of 10.
ISSNs are assigned by national and regional centers of the international ISSN Network, and each ISSN is unique to one serial publication. Separate ISSNs are needed for serials in different media, so print and electronic media versions of a serial need separate ISSNs, and CD-ROM versions and web versions require different ISSNs. However, the same ISSN can be used for different file formats (e.g. PDF and HTML) of the same online serial.
ISSNs are used in ordering, cataloging, interlibrary loans, and other practices in connection with serial literature. In many countries, an ISSN is mandatory for all publications subject to the legal deposit.
