What is an ISBN?

An ISBN, or International Standard Book Number, is the identifier the book trade uses to tell one edition of a book apart from every other. Since 2007 every new ISBN has 13 digits (older ones had 10), and it is printed on the copyright page and, as a barcode, on the back cover of print books. Bookstores, distributors, libraries and wholesalers all use it to order, stock and track sales.

Each format needs its own ISBN. Your paperback, hardcover, eBook and audiobook are separate products, so they each get a separate number. A new edition with substantial changes also needs a new ISBN; fixing a typo usually does not. The ISBN also records who the publisher is, which is why the imprint name you register it under matters.

ISBNs are issued by one national agency per country, and prices and procedures differ. In the US they are sold by Bowker; in the UK by Nielsen. In India, ISBNs are issued by the Raja Rammohun Roy National Agency for ISBN, which has offered them free of charge through its online portal — check the agency's current process before applying. Some platforms, including Amazon KDP and Draft2Digital, offer a free ISBN, but a platform-assigned number typically lists that platform as the publisher and may only be usable through it, so check the platform's current rules.

Kindle eBooks sold only on Amazon do not need an ISBN, because Amazon assigns its own ASIN. Print books sold through retailers do.