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National ISSN Centre
Biblioteca Nacional de Portugal
Campo Grande, 83

1749-081 Lisboa

Tel. 21 7982012 / 13 / 406
Fax 21 7982432
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National ISSN Centre

What is an ISSN?
An ISSN is a numeric code that constitutes an unequivocal identifier for each serial publication. Its component parts have no special meaning in their own right. The ISSN is defined in ISO 3297: 2007 - Information and Documentation. International Standard Serial Number ISSN, which is managed by theISSN International Centre.

How is an ISSN made up?
An ISSN is composed of two groups of four digits separated by a hyphen, which have no special meaning in their own right. The eighth digit is a control character which an algorithm calculates from the previous numbers. This control character may be X when its value is equal to 10.

What publications does ISSN apply to?
The ISSN system applies to every serial publication, whether it has already been published, is currently being published, or is going to be published in the predictable future. Serial publications comprise journals and magazines, newspapers, annual publications (such as reports and accounts, yearbooks, directories, etc.), monographic series, memoires, company minutes and so on, whatever their carrier.

How to obtain an ISSN
The first thing is to find out whether the publication is a serial publication. If necessary, contact the National ISSN Centre for clarification. The ISSN application must be accompanied by the information requested on the respective form (title, publisher, date of publication of the first issue, periodicity, and the director/coordinator of the publication). The ISSN attribution service is entirely free of charge.