The short answer
- What it is: the International Standard Book Number, a unique ID for a specific edition and format of a book.
- How long: 13 digits since 1 January 2007. Older books have 10-digit ISBNs.
- What the digits mean: a prefix (978 or 979), a country or language group, the publisher, the title and format, and a check digit at the end.
- Who issues them: one national agency per country. In the US that's Bowker; in the UK, Nielsen. Canada gives them out free.
- What it costs in the US: $125 for one, $295 for 10, $575 for 100 from Bowker. Amazon KDP gives free ones for print books it publishes.
- What it isn't: copyright. An ISBN identifies a book; it doesn't protect it.
| Digits | Our example: 979-8291663530 | What it means |
|---|---|---|
| Prefix | 979 | Marks the number as a book (978 or 979). 978 is the original block; 979 was opened when 978 started running out |
| Registration group | 8 | The country or language area. 979-8 is the United States; 978-0 and 978-1 are English-speaking countries; 978-93 is India |
| Registrant and publication | 29166353 | The publisher's block and this one title in this one format. The split between the two varies with the size of the publisher's block |
| Check digit | 0 | Calculated from the other 12 digits, to catch typing errors |
That number is the paperback of 365 Days of Tao by Dae Lee, one of ours. The hardcover and the Kindle edition are separate products, and each has its own identifier.
How the check digit works
Take the first 12 digits. Multiply them alternately by 1 and 3, starting with 1, and add everything up. The check digit is whatever brings the total up to the next multiple of 10.
For 979829166353: 9×1 + 7×3 + 9×1 + 8×3 + 2×1 + 9×3 + 1×1 + 6×3 + 6×1 + 3×3 + 5×1 + 3×3 = 140. That's already a multiple of 10, so the check digit is 0, and the full ISBN is 9798291663530.
A single wrong digit, or two neighbouring digits swapped, almost always gives a different result, so a shop's system rejects the number before ordering the wrong book. The 13-digit ISBN is also an EAN-13 barcode number, which is why the barcode on the back of a book and the ISBN on the copyright page match.
ISBN-10 vs ISBN-13
Before 2007, ISBNs had 10 digits and a different check digit, which could be X (meaning 10). Every 10-digit ISBN converts to a 13-digit one: put 978 in front, drop the old check digit, and calculate a new one. A 979 ISBN has no 10-digit form. Sites still show both for older books, and they point to the same edition.
Which books need their own ISBN
- Each format: paperback, hardcover, large print, ebook and audiobook each get a separate ISBN, if they use one at all.
- Each new edition: a revised text, a new translation, or a new publisher means a new ISBN.
- Not a reprint: printing more copies of the same edition keeps the same number. So does fixing a few typos.
- Kindle ebooks: Amazon doesn't require one. It assigns its own ASIN, a 10-character ID that only Amazon uses.
A licensed edition shows the rule clearly. Bloomsbury publishes 365 Days of Philosophy by Dae Lee in South Asia from October 2026 under its own ISBN, 9789369522422. The group digits are 93, for India, and the rest identify Bloomsbury's block and the title. Same book, different publisher and market, so a different number.
How to get an ISBN
Buy from your country's agency, not a reseller. A reseller's ISBN registers the reseller as the publisher, and you can't move it later.
- United States: Bowker, through myidentifiers.com. $125 for one, $295 for 10, $575 for 100, $1,500 for 1,000. Check the site, since prices change.
- Canada: free, from Library and Archives Canada.
- UK and Ireland: Nielsen.
- Elsewhere: the International ISBN Agency (isbn-international.org) lists every national agency.
- Free through a platform: Amazon KDP gives a free ISBN for paperbacks and hardcovers. It can only be used for that edition on KDP, and the publisher shows as "Independently published" unless you supply your own.
If you'll publish more than two books, or more than one format, the 10-pack is cheaper per book than buying singles.
How to look up a book by ISBN
Paste it into any bookshop search, Google Books or WorldCat, the shared library catalogue. With or without hyphens works. If a search finds nothing, check the digits with the method above: a wrong check digit means a typing error.
For the rest of a book's anatomy, from the copyright page to the colophon, see the parts of a book.
Common questions
What is an ISBN?
The International Standard Book Number: a 13-digit number that identifies one edition of a book in one format from one publisher. Bookshops, libraries and distributors use it to order and catalogue books.
What do the numbers in an ISBN mean?
A 978 or 979 prefix, a registration group for the country or language, a publisher block and title number, and a final check digit. In 979-8291663530 (the paperback of 365 Days of Tao), 979 is the prefix, 8 is the United States, and 0 is the check digit.
How much does an ISBN cost?
In the US, Bowker sells them at $125 for one, $295 for 10 and $575 for 100. Canada issues them free. Amazon KDP gives free ISBNs for print books published through it, usable only on KDP.
Do ebooks need an ISBN?
Not on Amazon, which uses its own ASIN. Other ebook stores and libraries often ask for one, and the ebook needs its own number, separate from the print edition.
What is the difference between ISBN-10 and ISBN-13?
ISBN-10 was used until the end of 2006. ISBN-13 adds a 978 or 979 prefix and uses a different check digit. Every ISBN-10 has a matching 978 ISBN-13 for the same edition.
Does an ISBN give you copyright?
No. Copyright exists as soon as the work is written. An ISBN only identifies an edition for the book trade.