An ISBN is a 13-digit number that identifies one edition of one book: the paperback, the hardcover and the ebook each need their own. It is how bookshops, libraries and distributors track a title. What confuses most first-time authors is not what an ISBN is, but whether they need to buy one at all.
If you publish an ebook only on Amazon KDP, you do not need an ISBN at all. Amazon gives every Kindle ebook its own ASIN identifier, and that is enough for it to sell on Amazon. Plenty of authors publish their first ebook this way and never buy an ISBN.
Amazon KDP and IngramSpark both offer a free ISBN for print books. The catch is control, not money. A free ISBN lists the platform, not you, as the publisher of record, and it usually cannot be used anywhere else. A free KDP paperback ISBN cannot be taken to IngramSpark or to another printer. If you later want the same book distributed widely under your own imprint name, you will need a new ISBN and a new edition.
Your own ISBN lists you, or your publishing imprint, as the publisher, and you can use it with any printer or distributor. That matters if you plan to sell the same print edition on Amazon and through IngramSpark, approach bookshops, or build a publishing brand under one name. In the US, one ISBN costs $125 from Bowker, with bundles cheaper per number. In some countries, such as Canada, ISBNs are free from the national agency. Prices and agencies differ by country, so check your own national ISBN agency before buying.
Ebook only on Amazon: no ISBN needed.
One print book, one platform, testing the waters: a free ISBN is fine, and you can switch to your own ISBN for your next book.
Same print edition everywhere, or your own imprint name on the record: buy your own ISBN before you publish that edition.
One warning that saves real money: never buy an ISBN from a reseller or a "publishing package" at a markup, and never reuse an ISBN from another book or edition. One ISBN belongs to one edition, forever.
Wecrafte publishes books end to end in ebook, paperback and hardcover, on the platforms you choose, with the setup handled for you. See wecrafte.com or write to info@wecrafte.com.
