This document defines and promotes the use of a standard code (ISSN) for the unique identification of serials and other continuing resources.Each International Standard Serial Number (ISSN) is a unique identifier for a serial or other continuing resource in a defined medium whether print or electronic.This document also allows for grouping related continuing resources into clusters identified by a separately-prefixed ISSN as defined in this document.ISSNs are applicable to serials and to other continuing resources, whatever the business model or modes of distribution (e.g. free, open access, on subscription, etc.) and irrespective of whether the serial is currently in publication, has ceased publication, or publication is planned for the foreseeable future. Continuing resources include whatever the medium of production (print or electronic):— serials, such as newspapers, periodicals, journals, magazines, blogs, conference proceedings, monographic series with no predetermined conclusion, annual or other periodic reports, and— ongoing integrating resources that are updated, such as loose-leaf publications, updating websites, institutional repositories, directories and databases.Monographs, sound and video recordings, notated music publications, audiovisual works, textual works and musical works have their own standard identifiers and are not specifically mentioned in this document. Such items can carry an ISSN in addition to their appropriate identifiers when they are part of a continuing resource.NOTE This document does not contain any operational guidance for its practical implementation.