ISBN-13 explained

An ISBN (International Standard Book Number) is an identifier used by the book trade to recognise a specific book product. Think of it like a SKU. It helps retailers, libraries and distributors avoid mixing up similar titles.

ISBNs identify a specific edition and format (paperback vs hardcover). They are not a “title ID”.

An ISBN contains number segments that indicate a book prefix, a region/language group, a publisher/imprint range, a publication/item number, and a check digit used to catch errors.

An ISBN does not contain your title, author name, price, copyright, or sales rank. That information exists in databases that use the ISBN.

ISBN-13 is often shown with hyphens to reveal its parts:

• Prefix (usually 978 or 979)
• Registration group (country/region or language area)
• Registrant (publisher/imprint identifier)
• Publication (specific title/edition item number)
• Check digit (math digit that catches typos)

Segment lengths vary by country and publisher range, which is why hyphen positions differ.

ISBN-10 is the older format. ISBN-13 is the modern standard and matches retail barcode systems. Many books display both, but ISBN-13 is what most current systems rely on.

ISBN-10 check digits can be X. ISBN-13 check digits are always 0–9.

Properly assigned, no. One ISBN should map to one specific book product (edition + format). If two different books appear to share an ISBN, you’re looking at a data error, a misassigned number, or a dodgy listing.

Reprints of the same edition often keep the same ISBN. A substantially revised edition should get a new ISBN.

Not all books have an ISBN. Some small print runs, private publications, zines, and niche products are sold without one. In most cases it is not illegal to sell a book without an ISBN.

Usually one of these:

• It was never assigned an ISBN (private or small-run publishing).
• It uses a platform identifier instead (internal product codes).
• It’s old (pre-standard adoption) or from a niche publisher.
• The ISBN exists but isn’t printed (rare, but possible).

Decide what you need it for.

• Retail/libraries/distribution: you almost certainly want an ISBN.
• Direct sales only: you may not need one.

If you want marketplace clarity: ISBN + consistent metadata + a front-cover Seal is a strong combination.

ISBNs generally do not “expire”. Once assigned to a specific product, they should remain associated with it, even if the book is out of print.

“Expired ISBN” claims usually confuse ISBNs with a service subscription, a database listing, or a platform rule.

Only if it was legitimately assigned to the same product you’re selling (same title, same edition, same format). You cannot recycle an ISBN from a different book.

There are two different “valid” checks:

• Math-valid: the check digit matches (catches typos).
• Market-valid: the ISBN is actually assigned to that title/format in databases.

A math-valid ISBN can still be wrong for the book if someone copied an ISBN from another listing.

That’s a printer’s key (number line). It indicates the printing. The lowest number present usually indicates the printing number.

• 10 9 8 7 6 5 4 3 2 1 often means first printing.
• If the 1 is missing and the lowest is 2, it’s typically second printing.

Publishers format number lines differently, but the “lowest number rule” is the usual guide.

Yes, you can buy ISBNs from the official ISBN agency for your country. Pricing varies and changes over time.

• Australia: single ISBN is commonly listed around AUD $44, with blocks reducing per-ISBN cost.
• United States: single ISBN is commonly listed around USD $125, with bulk packs cheaper per unit.

In professional publishing, yes. Each format (paperback, hardcover, audiobook, etc.) typically needs its own ISBN. This prevents supply-chain confusion and keeps ordering accurate.

This is where the front-cover Seal helps: it keeps attribution tied to a specific record and format, not a vague “trust me” claim.