Do I need an ISBN, and what happens with a translated book

An ISBN (international standard book number) is the long number printed under the barcode on the back of a book. For a digital book on Amazon it is optional; for a printed book it is required, and Amazon supplies one at no charge. That is the summary, and for most authors it is enough.

The part that does deserve attention is what happens when you publish the book in an additional language, because that is where the numbers multiply in a way that surprises people.

What the number does

Think of it as a model number. Two books can share a title, and two authors can share a name. The number is the only thing that tells them apart with certainty.

Thanks to it, a bookshop can order exactly the edition a customer asked for, a library knows what is on its shelves, and a reporting system can add up sales of the same book across several different shops.

In a world where most of your sales happen on one website, the number matters less. The moment you want to step outside that website, it becomes necessary.

When it is required and when it is not

According to Amazon's own help page on the subject, the number is optional for digital books and required for printed ones, both softcover and hardcover.

For a printed book Amazon offers a number of its own at no charge. It carries one limitation worth knowing: it can only be used to publish through Amazon. If in a year you want to print that same edition through somebody else, you will need a new number.

The second difference is the publisher name shown beside the book. With Amazon's number, a generic name indicating independent publication is recorded. With your own number you can record a name of your own — and that matters to anyone who wants the book to look like a proper imprint.

Why a translated book doubles the count

Here is the surprise. That same Amazon page states that a number cannot be reused across different formats or across new editions. A translation is not quite a new edition — it is a different book.

The practical result: your novel in its original language is one book. The same novel in English is a second book. If each of them appears in both digital and print, you already have four separate items.

This is not only bureaucracy. It also explains why reviews do not travel between versions, and why the translated book starts life with no history. We went into that in what Amazon's platform does with your book.

So what should you do

If you are publishing a first book and only want to see what happens, take what Amazon gives you and think about it no further. It is the least important part of your day.

If you are building something long-term — a series, an imprint name, several languages, sales outside Amazon — it is worth buying numbers of your own from the agency in your country. In some countries they are issued at no cost through the national library, and in others you buy them from a commercial agency.

Either way: do not let the number hold you up. Nobody ever failed to publish a book because of an ISBN, and a great many authors spend weeks on it that would have been better spent checking the translation itself. If you are in the middle of a decision like that, our frequently asked questions help put the steps in order.