Explaining DOIs, ISBNs, ISSNs & Other Publication Identifiers

Explaining DOIs, ISBNs, ISSNs and Other Publication Identifiers

1. Why Publication Identifiers Matter

The volume of academic and professional information produced today is staggering. Every year, publishers and institutions release countless books, journal articles, conference proceedings, technical reports, datasets, recordings, films, and digital resources. For researchers, librarians, and students, the main challenge is no longer scarcity of information, but finding and correctly identifying the exact item they need among millions of similar-looking titles.

This is where publication identifiers come in. These codes—strings of digits and sometimes letters—were created to solve very practical problems:

• How do we distinguish one edition of a book from another?
• How can a library catalogue, a database, or a bookstore always point to the correct journal or article?
• How can a citation link reliably to the right web page, even if the publisher’s website changes?
• How can royalties and rights be tracked across multiple formats, editions, and territories?

Identifiers such as the ISBN (International Standard Book Number), ISSN (International Standard Serial Number), and DOI (Digital Object Identifier) have become part of the infrastructure of scholarly communication. Other codes, such as ISMN for printed music or ISRC for sound recordings, ensure that works in different media can be tracked and referenced just as precisely as textbooks or journal articles.

This article explores the most common identifiers you are likely to encounter as a researcher or author. It explains what each one is for, how it is structured, and how to use it correctly in your own work.

2. ISBN – International Standard Book Number

The ISBN is probably the best-known publication identifier. It is used worldwide to identify books and book-like publications such as monographs, book series, and sometimes conference proceedings.

2.1 What an ISBN Identifies

An ISBN does not identify a “work” in the abstract; it identifies a specific format and edition. That means:

• a hardback edition and a paperback edition of the same title have different ISBNs;
• if a book is available as EPUB, MOBI (Kindle), and PDF, each digital format can be assigned a different ISBN;
• a revised edition with updated content will receive a new ISBN, even if the title looks similar to the earlier edition;
• a simple reprint of the same edition usually reuses the existing ISBN.

Multi-volume sets illustrate this principle well: each volume may have its own ISBN, and the set as a whole can also have an additional ISBN representing the complete package.

2.2 Structure of the ISBN

Since 2007, ISBNs have consisted of 13 digits, usually shown with hyphens. Older publications may still display the earlier 10-digit format, which remains valid and can be mapped to the newer style.

A 13-digit ISBN typically has five parts:

1. Prefix – either “978” or “979”.
2. Registration group – identifies a country or language group (e.g. English-language, German-speaking regions, etc.).
3. Registrant – identifies the publisher or imprint.
4. Publication element – identifies the specific title or edition.
5. Check digit – used to detect transcription errors.

These elements are often separated by hyphens (e.g. ISBN 978-1-2345-6789-7). The lengths of the individual segments vary, which is why guessing where to insert the hyphens is not always straightforward. The check digit is calculated using a defined formula and may be an “X” in the older 10-digit system, representing the value 10.

2.3 Where to Find the ISBN

For printed books, the ISBN usually appears:

• on the back cover, often above the barcode;
• on the copyright or publication details page near the front of the book;
• in online catalogues and product descriptions.

For e-books, you will typically find the ISBN on the copyright page inside the file and in the metadata provided by the publisher or e-book retailer. Audio-books delivered on physical media (e.g. CD, DVD) may also carry ISBNs, though this is not universal.

3. ISSN – International Standard Serial Number

While ISBNs are used for books and monographs, the ISSN identifies serial publications—continuing resources issued in successive parts, such as:

• scholarly journals and magazines;
• newspapers;
• annual reports and yearbooks;
• series of conference proceedings;
• ongoing online publications and some blogs.

3.1 Print ISSN, Electronic ISSN, and ISSN-L

An ISSN consists of eight digits, typically shown as two groups of four separated by a hyphen (e.g. ISSN 1234-567X, where the final “X” can again represent the value 10). Unlike the ISBN, the ISSN does not encode information about country or publisher; it is simply a serial number associated with a particular title.

The ISSN system makes an important distinction between:

• p-ISSN (print ISSN) – assigned to the print version of a serial;
• e-ISSN (electronic ISSN) – assigned to the online or electronic version.

To connect different media versions of the same serial, the system also uses an ISSN-L (linking ISSN). This is a single ISSN that acts as the “master” identifier for all formats of a given serial. Usually, the first ISSN assigned to a serial becomes the ISSN-L.

3.2 Where the ISSN Appears

For print serials, the ISSN is often printed on the front cover (commonly in the upper corner) and on the page containing publication information. For electronic journals, you will usually find it:

• on the journal’s homepage or “About” page;
• in database listings and library catalogues;
• in PDF article headers or footers.

If a journal changes its title significantly, it must obtain a new ISSN, because the ISSN is tied to the title, not the publisher or subject area.

Note that a journal volume or special issue can sometimes carry both an ISSN (for the serial) and an ISBN (when it is also marketed as a standalone book). Both identifiers are valid and serve different cataloguing purposes.

4. DOI – Digital Object Identifier

The DOI has become the standard way to identify digital research objects. Unlike ISBNs and ISSNs, which are tied to the physical or serial nature of a publication, DOIs are content-based, persistent identifiers for virtually any type of digital object.

4.1 What a DOI Identifies

Common examples of items that may carry a DOI include:

• journal articles and their components (tables, figures, supplementary material);
• book chapters and sometimes entire books;
• datasets, code repositories, and software versions;
• conference papers and presentations;
• reports, preprints, and working papers;
• audio, video, and image files used as research outputs.

A single publication can contain multiple DOIs at different levels: one for the journal or book, another for an issue or volume, and additional DOIs for individual articles or chapters.

4.2 Persistence and Resolution

Three features make DOIs particularly useful:

• Uniqueness – each DOI is assigned to a single object.
• Persistence – the DOI will always refer to that object, even if the object moves to a new web address.
• Resolvability – a DOI can be “resolved” via a resolver service (most commonly, https://doi.org/), directing users to the current location of the object or at least its metadata.

For example, the DOI 10.1017/S0362152900011995 can be turned into a persistent URL by prefixing it: https://doi.org/10.1017/S0362152900011995. If the publisher moves the article to a different site, they update the DOI metadata rather than changing the DOI itself, so the link continues to work.

4.3 DOI Structure

Formally, each DOI has the structure:

prefix/suffix

The prefix begins with “10.” (which marks the DOI namespace) followed by a registrant code that identifies the organisation (e.g. publisher or data centre) that registered the DOI. The suffix is chosen by the registrant and may include letters, numbers, parts of ISSNs or ISBNs, and internal codes. For example:

10.1017/S0362152900011995

• 10.1017 – prefix and registrant (here, associated with a particular publisher);
• S0362152900011995 – suffix representing the specific article.

When you cite a source, including the DOI (formatted as a URL) in your reference list makes it much easier for readers and reference managers to locate the exact item.

5. Article- and Component-Level Identifiers: SICI, BICI, and PII

5.1 SICI – Serial Item and Contribution Identifier

Before DOIs became widespread, the Serial Item and Contribution Identifier (SICI) was developed as a way to identify individual parts of serials—such as specific issues, articles, or even abstracts—by extending the ISSN. A SICI code is relatively long and complex, containing segments for:

• the serial’s ISSN and publication date;
• volume and issue numbers;
• the starting page or location of the contribution;
• a code derived from the article title;
• control characters that describe the type and format of the item, plus a check character.

A SICI might once have been used as part of a DOI suffix or in Uniform Resource Names (URNs). However, because SICI syntax includes characters such as colons that can cause technical problems, registration agencies such as Crossref no longer recommend SICIs as DOI suffixes. In practice, DOIs have largely replaced SICI codes for article-level identification, but you may still see them in older systems or legacy records.

5.2 BICI – Book Item and Component Identifier

The Book Item and Component Identifier (BICI) is conceptually similar to SICI, but designed for book components rather than serials. In theory, a BICI extends the ISBN of a book to identify a specific chapter, section, or other component. It follows a three-part structure (item, component type, control segment) modeled on SICI.

Although the standard was proposed to improve citation and tracking of book chapters, BICI has not been as widely adopted as ISBN-plus-DOI combinations. Today, publishers more often assign independent DOIs to chapters and rely on the ISBN for the book as a whole.

5.3 PII – Publisher Item Identifier

The Publisher Item Identifier (PII) is another historical identifier found in some scientific journals and books. A PII is a 17-character code that embeds the ISSN (for journals) or ISBN (for books), plus extra characters to indicate publication type, year, an item number, and a check digit. For example:

• the first character indicates whether the source is a serial (“S”) or a book (“B”);
• the next 8 or 10 digits are the ISSN or ISBN;
• two digits may give the year (for serials);
• four digits identify the item within that serial or book;
• the final character is a check digit.

In modern publishing, DOIs usually perform the role that PIIs were designed for, but you may still encounter PIIs in older articles or as internal publisher references.

6. Identifiers for Textual Works and Electronic Texts: ISTC and ETTN

6.1 ISTC – International Standard Text Code

The International Standard Text Code (ISTC) aims to identify a text-based work itself, not a particular edition or format. While an ISBN refers to a specific published version (e.g. hardback 2nd edition), an ISTC is associated with the underlying content as a work: the narrative or text that might appear under different titles, translations, or formats.

An ISTC is a 16-character hexadecimal code (using digits 0–9 and letters A–F), usually displayed as:

ISTC 0A9-2002-12B4A105-7

Its structure typically includes:

• a registration element (assigned by the agency);
• the year of registration;
• a work identifier segment;
• a check digit.

ISTCs are especially useful for rights management, aggregations, and cataloguing where many editions, translations, and formats share the same underlying text.

6.2 ETTN – Electronic Textbook Track Number

The Electronic Textbook Track Number (ETTN) is a unique identifier developed to track purely electronic texts—such as e-books, electronic proceedings, or digital journals—at the file level. An ETTN is a 13-digit numeric code comprising:

• three digits to indicate the subject or focus of the text;
• two digits for the year the ETTN was assigned;
• five digits as a unique text identifier;
• two digits for the month of assignment;
• a final check digit.

ETTNs are less widely known than ISBNs or DOIs, but they illustrate ongoing efforts to manage digital publications with precision, especially in educational contexts.

7. Historical and Commercial Identifiers: SBN and ASIN

7.1 SBN – Standard Book Numbering

Before the ISBN system was standardised internationally, some publishers used the Standard Book Number (SBN), a 9-digit identifier. When ISBNs were introduced, an SBN could be converted to a 10-digit ISBN simply by adding a leading zero. The check digit remained unchanged, so the conversion required no recalculation.

Today you may still encounter SBNs in older catalogues or on very old editions. Adding a leading zero allows them to be used in systems expecting a 10-digit ISBN.

7.2 ASIN – Amazon Standard Identification Number

The ASIN is a proprietary identifier used by Amazon to manage products on its platforms. It consists of ten characters (letters and numbers), for example B01DUV1T00. Every product sold through Amazon has an ASIN; for books, the relationship between ASIN and ISBN is particularly notable:

• for printed books with a 10-digit ISBN, the ASIN is usually identical to that ISBN;
• for Kindle editions and other products that do not carry ISBNs, Amazon assigns a unique ASIN.

ASINs are mainly relevant for marketing, sales, and Amazon search; they are generally not used in academic citations, where ISBNs and DOIs remain the preferred identifiers.

8. Identifiers for Music and Audio-Visual Content: ISMN, ISRC, ISWC, ISAN

8.1 ISMN – International Standard Music Number

The ISMN identifies printed or notated music (scores, parts, and similar materials), whether published in print or digital formats. Its logic is similar to the ISBN: each separate edition or part of a musical work receives its own ISMN.

Originally, ISMNs were 10-character codes beginning with “M” followed by digits for publisher, item, and check digit. Since 2008, ISMNs have moved to a 13-digit structure, starting with the prefix “979-0” followed by publisher and item blocks plus a final check digit:

ISMN 979-0-XXXX-XXXX-X

A single publication, such as a music book that contains both textual commentary and full scores, may carry both an ISBN and an ISMN, allowing it to function within book and music publishing systems simultaneously.

8.2 ISRC – International Standard Recording Code

The International Standard Recording Code (ISRC) uniquely identifies a specific sound recording, not the underlying musical work. Different performances, mixes, and versions of the same song have different ISRCs.

An ISRC consists of 12 characters and is typically represented as:

ISRC CC-XXX-YY-NNNNN

• CC – country code;
• XXX – registrant code (usually representing the label or producer);
• YY – last two digits of the year the ISRC was assigned;
• NNNNN – a unique sequence number for the recording within that year.

ISRCs remain constant across platforms and releases, making them crucial for royalty tracking, copyright management, and digital distribution.

8.3 ISWC – International Standard Musical Work Code

While the ISRC identifies a particular recording, the International Standard Musical Work Code (ISWC) identifies a specific musical work—for example, a composition by a songwriter—regardless of how many recordings or publications exist.

An ISWC typically appears as:

T-123.456.789-0

• a prefix character (usually “T” for musical works);
• nine digits grouped with dots for readability;
• a check digit.

Unlike some identifiers, the ISWC does not encode information about the composer or publisher; it is simply a unique work number allocated sequentially. It supports rights management and helps collecting societies track performances and uses of the underlying composition.

8.4 ISAN – International Standard Audiovisual Number

The International Standard Audiovisual Number (ISAN) applies to audiovisual works such as films, television programmes, video games, advertising spots, and some live broadcasts. An ISAN is assigned to the work as a whole, not just to one specific edition or version.

Once an ISAN is registered for a work, it can be used across multiple formats and releases:

• the original cinema release of a film;
• international versions and language dubs;
• director’s cuts and extended editions;
• DVD and Blu-ray releases;
• streaming versions and promotional clips.

ISAN codes are fairly long and usually presented with the “ISAN” prefix and grouped by hyphens for readability. They are essential in rights management, scheduling systems, and multilingual distribution pipelines.

9. Practical Tips for Researchers and Authors

9.1 Where to Find Identifiers

When preparing a bibliography, reference list, or metadata for your own work, you can typically locate identifiers here:

• ISBN: back cover, copyright page, publisher’s website, library catalogue, or book retailer listing.
• ISSN: journal cover, “about” page on the journal website, article PDF header, or database record.
• DOI: first page of the article, article landing page on the publisher’s site, or in database metadata.
• ISMN, ISRC, ISWC, ISAN: often recorded in specialist databases, catalogues, or rights-management systems rather than in everyday citation formats.

9.2 Using Identifiers in Citations

Most major citation styles now encourage including DOIs and ISBNs where available. Good practice includes:

• formatting DOIs as URLs (e.g. https://doi.org/...);
• providing the ISBN for books and edited volumes, especially in reference lists and book reviews;
• using the ISSN primarily in cataloguing or journal descriptions rather than in individual article citations.

9.3 Avoiding Common Mistakes

Researchers frequently encounter issues such as:

• confusing ISBN and ISSN or using one where the other is required;
• copying an incomplete or mistyped DOI and wondering why the link fails;
• omitting the DOI even when the publisher provides one, making sources harder to locate;
• using an ASIN instead of an ISBN in an academic reference.

Taking a moment to double-check identifiers in reliable databases or directly on the publisher’s site prevents these problems and improves the reliability of your references.

10. Conclusion

Publication identifiers are easy to overlook, but they are fundamental to the way scholarly communication works. Codes such as ISBN, ISSN, and DOI allow libraries, databases, search engines, and readers to distinguish between hundreds of thousands of near-identical titles, track relationships between formats and editions, and maintain stable links to digital content over time.

For researchers, a basic understanding of these identifiers is part of professional practice. Knowing which code applies to which type of resource—and where to find and use them correctly—helps you build accurate citations, manage your own publications more effectively, and ensure that your work can be discovered and cited reliably by others. As the volume and variety of scholarly outputs continue to expand, these small strings of numbers and letters will remain key to keeping the global research record organised and accessible.