The persistent identifier most familiar to today’s researchers is the DOI, attached to journal articles, datasets and a growing range of outputs. But the idea of giving a publication a stable, standardised identifier is far older, and two of the most successful examples predate the digital scholarly record by decades. The ISBN and the ISSN — the identifiers for books and for serials respectively — are international standards that quietly organise the worlds of publishing, libraries and the book trade, and they remain essential to the scholarly record, particularly for the monographs and journals that the article-centric DOI does not directly address. Understanding what each one identifies, and how they relate to the newer identifiers, is part of being literate in the persistent identifiers domain of the CASRAI Dictionary.
The ISBN: identifying books
The International Standard Book Number (ISBN), defined by the international standard ISO 2108, identifies a specific book or book-like product. The key word is specific. An ISBN identifies a particular edition in a particular form: a hardback, a paperback and an e-book of the same title each receive their own distinct ISBN, because they are different products that a bookseller, library or reader needs to distinguish. This granularity reflects the ISBN’s origins in the book trade, where ordering, stocking and selling demand that each product be unambiguously identifiable. For scholarship, the ISBN matters above all for the monograph — the scholarly book that remains a primary form of output in the humanities and many social sciences — giving the book-length output a stable handle comparable to the article’s.
The ISSN: identifying serials
The International Standard Serial Number (ISSN), defined by ISO 3297, identifies a serial — a publication issued in a continuing sequence, such as a journal, magazine or other periodical. Here the unit of identification is different and important to grasp. An ISSN identifies the title as a whole, the ongoing publication itself, not any single issue or article within it. The journal has one ISSN that persists across all its issues and volumes; individual articles are identified by other means. The ISSN system also handles the reality that serials appear in different media: a journal published in both print and online forms is typically assigned distinct ISSNs for each, with a linking mechanism connecting them as expressions of the same title. The ISSN lets libraries, indexes, agents and discovery systems refer to a journal unambiguously across decades and across changes of publisher or format.
How they differ from DOIs
The crucial conceptual point is that these identifiers operate at different levels of granularity, and they complement rather than compete with one another:
- An ISSN identifies a journal — the whole continuing publication.
- An ISBN identifies a book — a specific edition of a specific title.
- A DOI typically identifies an individual item — a single article, chapter, dataset or other discrete output — and is designed above all to resolve to a current location online.
Seen this way, the question is not which identifier is “better” but what each is for. The ISSN and ISBN identify the container or the work at the level of the journal title or the book; the DOI identifies the individual item and provides actionable resolution — click a DOI and it takes you to the thing. A complete picture of a scholarly book chapter might involve the ISBN of the book, the ISSN of a series it belongs to, and a DOI for the chapter itself, each doing its own job.
How they connect
These systems increasingly work together rather than in isolation. A DOI registered for a journal article carries metadata that includes the journal’s ISSN, tying the item-level identifier to the title-level one. A DOI for a book chapter can reference the book’s ISBN. This linking lets discovery and citation systems assemble a coherent view: knowing that this article (DOI) appeared in that journal (ISSN), or that this chapter (DOI) belongs to that book (ISBN). The identifiers form a layered structure — title-level and item-level — and the value comes from the connections between the layers. For monographs in particular, the maturing of book-level DOIs alongside the long-established ISBN has helped scholarly books participate more fully in the citation and discovery ecosystem articles have long enjoyed.
Why this matters for the record
Getting these identifiers right is not pedantry; it is what makes the scholarly record navigable. Accurate ISSNs let a journal’s entire run be tracked and its articles correctly attributed to it; accurate ISBNs let scholarly books and their editions be found, ordered, preserved and cited; and the connection of both to DOIs lets the item and its container be linked. Where these identifiers are missing, wrong or inconsistently recorded, citations break, holdings are confused and outputs become harder to find — problems that fall especially hard on book-based disciplines. The wider persistent-identifier landscape, from ORCID for people to ROR for organisations, is the subject of much of this domain, and the ISBN and ISSN are among its oldest and most reliable members.
A consistent vocabulary for identifiers
For these identifiers to do their work across publishers, libraries, indexes and research systems, the metadata around them must be described consistently — which identifier type is which, what it identifies, and how the levels relate. That consistency is what the CASRAI Dictionary provides: a shared vocabulary so that an ISBN, an ISSN and a DOI are each understood for what they are wherever they appear. And because every book and journal rests on the contributions of authors, editors and others, the work behind them can be described in the same shared framework — the CRediT taxonomy. Long before the digital age, the ISBN and ISSN showed the power of giving publications stable, standardised identities; they remain quietly indispensable to a scholarly record that now spans articles, books, journals and far beyond.