If you have ever looked up your journal on the ISSN Portal, you may have been surprised to find not one number but several — something like this:

ISSN: 1808-057X
ISSN-L: 1519-7077
ISSN-H: 9120-4690

Add in the “Print ISSN,” “Online ISSN,” and “eISSN” labels you see scattered across databases, indexing services, and your own OJS settings, and a perfectly reasonable question follows: which one is my journal’s “real” ISSN, and what is the difference between all of them?

The short answer is that these are not competing numbers. They are different types of ISSN that describe the same publication from different angles. Once you know what each letter stands for, the picture becomes simple. Here is the full breakdown for journal editors and publishers.

First, what an ISSN actually is

An ISSN (International Standard Serial Number) is an eight-digit code that identifies a continuing resource — a journal, magazine, newspaper, or any publication issued over time. It is written as two groups of four characters separated by a hyphen, and the last character can be an X (used when a check-digit calculation lands on the value 10).

Two things are worth remembering:

1. An ISSN carries no meaning of its own. It does not encode the country, subject, publisher, or quality of a journal. It is purely an identifier.
2. Each medium gets its own ISSN. This is the key to understanding everything below. A journal that exists in print and online is, from the ISSN system’s point of view, two versions of the same work — and each version is assigned a separate number.

That second point is exactly why a single journal ends up with multiple ISSNs.

Print ISSN (p-ISSN) and Online ISSN (e-ISSN / eISSN)

These are the two you will encounter most often.

• Print ISSN (p-ISSN) identifies the printed edition of the journal.
• Online ISSN (e-ISSN) identifies the electronic/online edition. You will also see this written as eISSN or “Online ISSN” — they all mean the same thing.

So if your journal publishes both a print and a digital edition, it correctly has two ISSNs. Neither one is more “official” than the other; they simply point to different formats of the same content.

Example: Journal of Open Publishing releases a printed volume and a PDF/online edition.
• Print ISSN: 2345-6780
• Online ISSN: 2345-6799
Both are valid. A library cataloguing the print copy uses the first; an indexing service harvesting the online articles uses the second.

This is also why indexing services such as DOAJ, Scopus, and Crossref often ask specifically for your e-ISSN — they are dealing with the online version.

ISSN-L: the “Linking” ISSN

Here is the problem the previous section creates: if one journal can have several ISSNs (print, online, maybe CD-ROM in the old days), how does anyone know they all belong to the same publication?

That is what the ISSN-L (Linking ISSN) solves.

The ISSN-L is a single ISSN chosen to group together all the medium versions of one work. No matter how many formats a journal has, it gets exactly one ISSN-L, and that number acts as the master link tying the print, online, and any other editions together.

In practice, the ISSN-L is usually identical to one of the journal’s existing ISSNs — most often the first one assigned (frequently the print edition).

Example, continued: Our Journal of Open Publishing now has:
• Print ISSN: 2345-6780
• Online ISSN: 2345-6799
• ISSN-L: 2345-6780 ← one number that represents “this journal, in any format”
When a database wants to merge the print and online records into a single journal entry, the ISSN-L is the value it uses.

If you only ever cite one number when you want to refer to the journal as a whole — regardless of format — the ISSN-L is a strong candidate.

ISSN-H: the “History” ISSN

This is the newest type, and the one most editors have never heard of. It was introduced with the latest version of the ISSN standard (ISO 3297:2020) and is still being rolled out across the ISSN Portal, so not every journal has one yet.

While ISSN-L groups versions across formats (print vs. online), ISSN-H (History ISSN) groups versions across time — specifically, the chain of titles a publication has carried over its lifetime.

Journals are renamed, merged, and split more often than people realize. A publication might begin life as Bulletin of Regional Studies, become Regional Studies Review, and later International Review of Regional Science — all genuinely the same ongoing journal, but each title change triggers a brand-new ISSN. Over the decades, one journal can accumulate four or five different ISSNs and catalogue records, which makes its history hard to follow.

The ISSN-H ties that whole succession of titles together under a single cluster identifier, so the entire lineage can be retrieved and even displayed as one connected history.

A practical thing to notice: ISSN-H numbers are newly minted cluster identifiers, not one of the journal’s everyday ISSNs. They currently appear in a distinctive range — you will often see them starting with a 9 (as in the 9120-4690 example at the top). That is your visual cue that you are looking at a history cluster, not a medium-specific number.

Don’t worry if your journal has no ISSN-H. Full assignment is an ongoing project. Its absence simply means the cluster hasn’t been generated for your title yet — it says nothing about the validity of your journal’s ordinary ISSNs.

Putting it all together

Going back to the example from the top of this article:

ISSN: 1808-057X → one specific medium version (here, the online edition)
ISSN-L: 1519-7077 → links all format versions of this journal together
ISSN-H: 9120-4690 → links this journal to its earlier/later renamed titles

Nothing is contradictory. You are looking at one journal described at three levels of grouping: a single edition, the family of formats, and the family of titles over time.

Quick reference

What this means for your OJS journal

If you run a journal on OJS (Open Journal Systems), your journal settings include fields for both a Print ISSN and an Online ISSN. A few practical pointers:

• If your journal is online-only (as most modern OJS journals are), fill in the Online ISSN (e-ISSN) and leave the Print ISSN empty. Do not invent or reuse a print ISSN you don’t actually have.
• Enter ISSNs in the correct field. Indexing services and harvesters read these values, and putting a print number in the online slot (or vice versa) causes mismatches in DOAJ, Crossref, and discovery databases.
• When an index, Crossref, or a DOI registration asks for the ISSN, it almost always wants your e-ISSN — the identifier for the version that is actually online.
• The ISSN-L is useful when you want a single value that represents your journal as a whole, independent of format.
• You generally won’t need to enter an ISSN-H anywhere in OJS; it is a portal-level cluster maintained by the ISSN International Centre, not something you assign yourself.

Getting these identifiers right is one of the quieter but more important parts of running a well-indexed journal — it is how the wider scholarly infrastructure knows that your print edition, your online edition, and your journal’s earlier names are all, in fact, you.

Need help configuring your journal’s metadata, ISSNs, or indexing settings in OJS? That’s exactly what we do at ojs-services.com.