The International Standard Serial Number (ISSN)is an eight digit number which identifies magazines and periodicals, including electronic publications. It is a unique identifier for each publication, assigned by the ISSN Center of the country where it is published. The ISSN uses a base-eleven numeric system, with 'X' used for '10'. It is often punctuated with a hyphen, although the only embedded information is the check digit at the end of the number. The punctuation adds no information to computer searches, and online sources typically omit it.
The ISSN differentiates periodicals without reference to their titles. This is useful for obtaining periodicals with short publication periods, out of print, similar titles published internationally, etc. The ISSN does not identify individual editions of periodicals. The edition (volume, number, date, etc.) must be provided when attempting ot order a periodical or article via interlibrary loan.