What is an ISSN? An International Standard Serial Number (ISSN) is an eight-digit code identifying one serial title, such as a journal, in one medium. Print and online editions get separate ISSNs, grouped under a linking ISSN (ISSN-L). An ISSN says nothing about quality. To verify one, test its check digit and read its ISSN Portal record.
An ISSN is registration, not indexing, as our decoder for journal indexing badges explains, and a missing one is a concern on the checklist for judging an unfamiliar journal. This guide covers the rest: how the number is built, why one journal can hold two, and how to read its record.
What is an ISSN made of: eight characters and a check digit
An ISSN is written as the letters ISSN followed by two groups of four digits joined by a hyphen: ISSN 0317-8471, for example. The eighth character is a check digit calculated from the first seven, and it can be the letter X.
The digits carry no meaning. Unlike an International Standard Book Number (ISBN), which contains country and publisher prefixes, an ISSN is what the ISSN International Centre calls an opaque identifier: it encodes nothing about the publisher or its location. Each ISSN is permanently linked to a key title, a standardised form of the title set by the ISSN Network. The standard behind it is ISO 3297, from the International Organization for Standardization (ISO).
A national ISSN centre assigns numbers to publishers in its own country; the ISSN International Centre covers countries without one. The publisher applies with proof of publication; the International Centre asks for pages showing the publisher's name and address. A print title can be requested up to three months before its first issue, and its record stays Provisional until the centre has checked that the title was published. Online titles are usually assigned a number only after publication: the International Centre waits for the first two issues and counts five articles as the minimum for a complete issue. The International Centre charges for its assignments; a national centre's terms are on its own site.
Print ISSN, eISSN and ISSN-L: one number per medium, one link between them
The register gives a title one ISSN per medium, so a print journal that launches an online version needs a second number for it. The labels eISSN, e-ISSN and online ISSN all mean the ISSN assigned to the online version; pISSN or print ISSN means the print one. They are one kind of number with a medium attached.
The linking ISSN groups the media versions of one title. It is not an extra number: the ISSN Network designates one of the existing ISSNs as the ISSN-L. Services such as library catalogues and search engines can use it to treat print and online as one title. A single-medium title still has an ISSN-L, identical to its own ISSN.
The ISSN International Centre's own teaching example shows the pattern. Dance research has a print record, ISSN 0264-2875, and an online record, ISSN 1750-0095, whose key title is Dance research (Online). Both records carry ISSN-L 0264-2875, the print number.
A journal holding two numbers should say which is which; citing ISO 3297, the International Centre suggests ISSN xxxx-xxxx (Online) and ISSN xxxx-xxxx (Print). A Crossref deposit makes the same distinction, and reading your article's Crossref record field by field shows where a mistyped one appears.
A new title needs a new ISSN; a new publisher does not
An ISSN belongs to a title, not to whoever owns it. The ISSN International Centre's guidance for publishers says a new ISSN is usually needed when a title changes. A change of publisher needs none unless the title changes with it. A change of medium, such as going online-only, needs a new number. A journal relaunched under its old title after a gap keeps its ISSN; one that returns to an earlier title gets a new ISSN, not the old one.
So a renamed journal has at least two records, one per title, and the free Portal view does not link them. Publishers, publication dates and related titles sit in the complete record, which the Portal opens to everyone only for titles in the Directory of Open Access Scholarly Resources (ROAD). Search the former title separately.
ISSN, ISBN and DOI identify three different things
| Identifier | What it labels | When a new one is issued | What the number itself encodes |
|---|---|---|---|
| ISSN | A serial title in one medium: the journal as a whole, not an issue or an article | A new medium, or a title change large enough to alter the key title | Nothing: no country, publisher or subject |
| ISBN | One book; each book in a series gets its own | Every new book, edition or format, such as a paperback or an EPUB | Country and publisher prefixes |
| DOI | One article, dataset or other object | Every new object; an existing DOI never changes, and the address it points to is updated instead | A prefix identifying the organisation that first registered it, such as a publisher |
An article can therefore carry a DOI of its own and, through its journal, an ISSN. Neither can stand in for the other.
Your reference list names the journal, not its ISSN
The sample references published by the US National Library of Medicine for the style of the International Committee of Medical Journal Editors (ICMJE) contain no ISSN. A journal article is cited by authors, title, abbreviated journal title, date, volume, issue and pages. If your target journal's instructions do not ask for an ISSN, leave it out.
The ISSN Network's part in a reference is indirect. Its International Centre maintains the List of Title Word Abbreviations behind ISO 4, a standard for abbreviating journal titles in citations. The number itself earns its place in metadata, where library catalogues and subscription agents use it to tell apart serials with similar names.
Check a journal's ISSN: the check digit, the record status, the medium
Three checks go beyond typing a number into a search box, and the first needs only arithmetic. The two numbers below are examples the ISSN International Centre itself uses; the mistyped version after them is invented.
- Take the first seven digits of ISSN 0317-8471: 0, 3, 1, 7, 8, 4, 7.
- Multiply them in turn by the weights 8, 7, 6, 5, 4, 3 and 2: 0, 21, 6, 35, 32, 12, 14.
- Add the products: 0 + 21 + 6 + 35 + 32 + 12 + 14 = 120.
- Divide by 11 and keep the remainder: 120 = 10 × 11 + 10, so the remainder is 10.
- Subtract the remainder from 11: 11 − 10 = 1. The eighth character must be 1, and it is.
- If the subtraction gives 10, the check character is X; if the remainder is 0, the check digit is 0. For ISSN 1050-124X the products total 56, the remainder is 1, and 11 − 1 = 10, hence the X.
A transposed pair fails. Typed as 0317-8741, the same steps give products of 0, 21, 6, 35, 32, 21 and 8, totalling 123: remainder 2, check digit 9, not the 1 printed. A passing check digit shows only that the number is well formed, not that anyone assigned it, or to which title.
Next, search the number in the ISSN Portal and read the free record with the table below. Comparing the record's title and web address with the site itself is a separate identity test, covered in how to tell whether a journal website is the real one.
| Field on the free record | What it means | What to check against the journal |
|---|---|---|
| Record status | Confirmed: the ISSN Network has checked that the title was published. The Portal's help pages also define Provisional (assigned before publication), Legacy (an early record, incomplete and not up to date), Cancelled, Suppressed (generally never published or not a continuing resource) and Unreported (not yet assigned). The free view shows core data for Confirmed records. | A journal claiming years of back issues should have a Confirmed record. A Legacy record is old, not suspect. |
| Key title | The standardised title the ISSN is permanently linked to, sometimes with a qualifier such as (Online) | It should match the journal's name, allowing for the qualifier. A different title means a different serial. |
| Title proper | The title as it appears on the publication | Small differences in capitals or punctuation are normal. |
| ISSN-L | The linking ISSN shared by the media versions of the title | The journal's print and online numbers should share it. If they do not, the register has not linked them; ask why. |
| Medium, and Other media where shown | Print, Online or another carrier, plus any other media the register links to the title | Compare with the label beside the number on the journal's site. An (Online) label on a number whose record says Print is a mislabel. |
| Other ISSN, such as a cancelled or incorrect ISSN | Numbers not valid for this title: a cancelled one, for example one assigned twice by mistake, or an incorrect one wrongly associated with it | A journal still printing one of these should switch to its valid ISSN. |
| Country and ISSN centre responsible | The centre that maintains the record | It should fit where the publisher says it is based. |
| Last modified | The date of the record's last update | An old date can explain a stale web address; it is not a fault in itself. |
Checking the ISSN of a Directive Publications journal
This post does not list our journals' ISSNs. Where one of our journals displays an ISSN, take it from the journal's home page, test its check digit, and compare its ISSN Portal record's status and medium with the label on the page. Where each Directory of Open Access Journals (DOAJ) criterion stands for us, including the match between register entry and journal title, is set out in our DOAJ application post. If a number on one of our pages fails the check digit, or its record names a different title or medium, report the problem to us.