What Is an ISBN?

How book numbers work, and why the right ISBN gets you the exact copy you want

An ISBN (International Standard Book Number) is a unique identifier assigned to a specific published edition of a book, not to "the book" as an abstract work. That distinction is the whole reason ISBNs are useful: they let you point at one exact edition, printing format, and publisher, out of what might be dozens of versions sharing a title.

ISBN-10 vs ISBN-13

You will see both formats, depending on how old the printing is:

• ISBN-10: the original format, 10 digits (the last can be the letter X), used for books published before 2007.
• ISBN-13: the current standard, 13 digits, starting with 978 or 979. Required for all books published from 2007 onward.

Every ISBN-10 has an equivalent ISBN-13 (add the 978 prefix and recalculate the final check digit), so the same physical book is often searchable both ways. Newer printings of older books may only carry the ISBN-13.

Why the same title can have many ISBNs

A new ISBN is assigned whenever the publication is meaningfully different, including:

• Format: hardcover, paperback, and audiobook editions of the same title each get their own ISBN.
• Publisher or imprint: a US edition and a UK edition from different publishers get different numbers, even with identical text.
• Edition: a revised or updated edition (new introduction, new cover, corrected text) gets a new ISBN; a reprint of the unchanged edition normally does not.
• Special editions: anniversary editions, movie tie-in covers, and box sets are usually separate ISBNs.

This is exactly why ISBN matters for collectors and careful buyers: searching by title can surface the wrong format or the wrong edition, while the ISBN pins down the one you actually want.

Where to find a book's ISBN

• The copyright page (usually the back of the title page), often printed as ISBN 978-0-....
• The back cover or dust jacket flap, frequently next to or below the barcode.
• The barcode itself: the digits printed under an EAN-13 barcode are the ISBN-13.

Using an ISBN to search

Because an ISBN identifies one exact edition, it is the fastest way to confirm you are comparing the same book across sellers, rather than accidentally comparing a paperback to a hardcover or a US edition to a UK one. Search any ISBN on BookBurglar and every result points at that specific edition, with a dedicated page and links to compare prices across Bookshop.org, Biblio, AbeBooks, ThriftBooks, and more.

Ready to look one up? Search BookBurglar by ISBN, title, or author to compare every seller in one place.