ISSNtunnus

ISSN tunnus, officially the International Standard Serial Number (ISSN), is a unique identifier for serial publications such as journals, magazines, and ongoing collections. It helps distinguish titles with similar names and supports consistent cataloging, retrieval, and linking across formats and publishers.

Format and check digit: An ISSN is an eight-digit code displayed as four digits, a hyphen, and four digits (for example 1234-5678). The last digit may be a numeral or the letter X, which represents 10 in the check-digit calculation. The check digit is determined by a modulo 11 calculation on the first seven digits with weights 8 through 2; the result is used so that the total is a multiple of 11. If the calculation yields 10, the check digit is X; if it yields 11, the check digit is 0.

Forms and administration: Many serials have separate ISSNs for print and electronic versions: the p-ISSN for print and the e-ISSN for electronic editions. Some titles share an ISSN across formats, others have distinct codes. The ISSN International Centre coordinates the Global ISSN Registry and oversees assignment of ISSNs through national centers.

Usage and scope: ISSNs are used in library catalogs, bibliographic databases, and publishing workflows to identify serials unambiguously, support cross-format linking, and facilitate metadata harvesting, citation, and ordering. They differ from ISBNs, which identify individual monographs, and from other identifiers such as DOIs. ISSNs identify serial titles rather than specific items, providing a stable reference for periodicals over time.