This article outlines the needs and benefits of reliable identifiers, in particular the ISSN, for the management of serial resources, particularly in the electronic world. The fundamental principles of the ISSN system, and the development of various recent uses of the ISSN are described to illustrate why that identification system is trusted at an international level, and who are today its main users. It concludes by mentioning the expanding role of identifiers in the electronic world.
ISSN stands for International Standard Serial Number. It is a standard code for the unique identification of serials "and other continuing resources" , defined by an ISO standard (ISO 3297) which was published for the first time in 1975 and is, since then, revised on a regular basis so as to take into account the changes occurring in this sector of the publishing industry.
In most cases users and readers know that newspapers, periodicals, journals, magazines are all "serials". But what is covered by "continuing resource" is less broadly known. According to the definition internationally adopted, it is "a publication, in any medium, that is issued over time with no predetermined conclusion, and made available to the public" . This definition covers both serials (which are published in discrete parts, usually bearing numbering) and all those publications and resources that are continuously added to or changed by means of updates that are integrated into the resource – such as databases, or websites. Indeed, ISSN numbers are applicable to a really broad range of publications, whatever their medium of publication or production (paper as well as electronic).
In the 70s, when the ISSN system was created, all serials were published in printed form. This has dramatically changed during the last fifteen years. Indeed, it is in the serial resources sector that electronic publishing has first become a reality. This has entailed fundamental changes in the production mode (all articles are now first produced in electronic form), in the content of the information (for instance, links to other contents are included in the article, which extends the content of the article itself, and induces new ways of reading and accessing the information), in the mode of issuance, in the distribution process, in the economic models of publishing, to cite only a few changes. It also made possible for new types of resources such as blogs, wikis, and many others to emerge.
An important characteristic of this fundamental change is the enormous increase in the number of resources which are made available on the internet: today it has become impossible for any publisher not to publish on the internet.
In this context, reliable identification, already important in the printed world , has become even more crucial – and the role of identifiers such as the ISSN is more important today than ever. To mention only one among many uses of the identifiers in the electronic world, managing the access to subscribed titles in a reliable way has become more and more of a challenge, and would not be possible without identifiers.
It is thus important to know precisely the characteristics of each identification system. ISSN numbers identify serial titles in a given format. ISSN are unique identifiers (one title in a given format = one ISSN number, one ISSN number = one title in a given format). ISSN numbers are persistent (once assigned, an ISSN is never re-assigned). They are independent from languages and scripts. All assigned ISSN numbers are accessible on the Internet via the international ISSN database, known as the "ISSN Register", which contains today more than 1,670,000 records .
The purpose of the ISSN system is the reliable identification of all kinds of serial resources worldwide, whatever the type of publication or production, the script, the language, or the medium of publication. To achieve this goal, the identification responsibility is shared among the ISSN network members. The ISSN network was created in 1975 by UNESCO and the French Government, and is made up today of 88 Member Countries , which share the identification responsibility on a national basis. All countries which are members of the ISSN system have the responsibility of creating their national ISSN centre, of identifying the serial resources published in their own country, of assigning ISSN numbers to those publications, and of sending the corresponding information to the ISSN International Centre in Paris, so as to make this information visible in the international ISSN database (the "ISSN Register"). This network organization has strong and obvious advantages – to mention just a few ones, the knowledge and establishment of links with the publishing community, the linguistic and cultural aspects, the links with the national organization of the legal deposit and with the scientific national information systems, cannot be better managed than by each concerned country. As in any international network, building consensus and a common professional vision and practice is fundamental within the ISSN network, particularly in the present period of huge changes in the sector of serial publication.
Those huge changes explain why exchanges in various professional contexts – such as the ACNP and NILDE meeting - are so important, for a better understanding of the needs and requirements of all the professional communities interested in the publishing, production, distribution, access to serial resources, and why maintaining strong relationships with all the professional communities served by the ISSN, including publishers, subscription agents, rights management organizations, scientific database producers, press distributors, libraries…and many others are so fundamental. Indeed, there has never been such a clear need for identification systems like the ISSN as today.
To illustrate this, and to conclude on the usefulness of the ISSN in the electronic world, an example should be taken and a citation should be made. The example regards the KEEPERS service , a new registry of archives for electronic journals which relies on the use of the ISSN as the key identifier for all titles electronically archived, the citation regards the report published by UKSG  and NISO  on "Knowledge bases and related tools" :
"Knowledge bases are key to the process of OpenURL linking because they not only know where content is, but they also know which versions of specific objects a particular institution's users are entitled to access. Knowledge bases are the only means by which users can be sure to reach an "appropriate copy."[…] "The accurate use of the ISSN is critical in ensuring successful resolution of OpenURL-based links".
The future is bright for all identifiers in the electronic world – particularly for the ISSN, where its main characteristics of quality, uniqueness and persistence make it the authoritative source of information for the identification of serial resources.
Françoise Pellé, ISSN International Centre, e-mail: firstname.lastname@example.org
 For the sake of simplification, in the rest of this article, "serial" will be used to designate the two categories of resources and should be understood as "serial and other continuing resources".
 ISO 3297 - Information and documentation - International standard serial number (ISSN), 4 th edition, 2007.
 To take only one example, ISSN numbers can be embedded into EAN-13 bar codes, with the 977 prefix which identifies serial publications in the GS1-EAN-13 world.