An ISSN is an 8-digit code used to identify newspapers, journals, magazines and periodicals of all kinds and on all media–print and electronic.
An ISSN (International Standard Serial Number) identifies all continuing resources, irrespective of their medium (print or electronic):
annual publications (reports, directories, lists, etc.),
In many countries, an ISSN is mandatory for all publications subject to the legal deposit.
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 result of the computing is equal to “10”, in order to avoid any ambiguity.