What an ISBN tells you about a book — and what it doesn’t
How ISBNs work, how to read the barcode on the back of a book, why the paperback and the hardcover have different numbers, why a reprint usually has the same one, and what to use for a book printed before ISBNs existed.
By the AllMyBooks team · Reviewed October 2026. Tell us through the Contact page if something here has changed.
What an ISBN is
An International Standard Book Number identifies one edition of a book in one format. It came into use around 1970, growing out of a nine-digit British scheme, and until 2007 it was ten digits long. Since the start of 2007 every new ISBN has thirteen digits and begins 978 or 979. A ten-digit ISBN and its thirteen-digit form name the same book: put 978 in front, and the last digit — a check digit calculated from the others — changes.
A ten-digit ISBN can end in X. It is not a typo: X stands for ten in the old check-digit scheme.
Reading the number
An ISBN is printed in hyphenated parts, and the parts mean something. After the 978 or 979 comes a registration group — a country or language area — then the publisher, then the book, then the check digit. 978-0 and 978-1 are the English-speaking group, 978-3 German, 978-91 Swedish; so the start of the number tells you where the edition was published, which is useful when two editions of the same title turn up side by side.
One ISBN per edition and format
- A hardcover, a trade paperback, a mass-market paperback, an ebook and an audiobook of the same text each get their own ISBN.
- A new edition — revised text, a new introduction, a different translation — gets a new ISBN.
- A reprint of the same edition normally keeps the same ISBN. That is why an ISBN cannot tell a first printing from a tenth: for that you need the number line on the copyright page.
- Publishers do not always follow the rules. Reused numbers, a hardcover and paperback sharing one, and book club editions printed with the trade edition’s ISBN or none at all all turn up.
The barcode on the back
The large barcode on the back cover is the thirteen-digit ISBN; the digits printed under it are the number itself. Many books carry a second, smaller five-digit barcode beside it. That one is the price: on American books a first digit of 5 means US dollars, so 51995 encodes a cover price of 19.95 US dollars, and 90000 means no price is encoded.
Mass-market paperbacks are the exception. They often carry a shop’s UPC barcode for the newsstand trade, with the ISBN printed separately — above the barcode, elsewhere on the back, or on the copyright page. If a barcode on a paperback does not look like an ISBN, look for the number that begins 978 or 0-.
Books printed before ISBNs
Books from before about 1970 have no ISBN. Many American books from the decades before carry a Library of Congress Control Number instead — printed on the copyright page as something like "Library of Congress Catalog Card Number 72-91684". It identifies the Library of Congress’s catalogue record for the book, and it is the closest thing an older book has to an ISBN. Without either, a book is identified by its title, author, publisher and year together — which is how antiquarian booksellers and libraries describe it.
Looking for an ISBN or a barcode for a book you have written? Each country has an ISBN agency that issues them to publishers and authors — in the United States, Bowker. This guide is about reading the numbers on books you own.