How ISBNs Actually Work

What actually happens if you can't buy your own ISBNs? I found out the hard way: I got blocked from the site I was planning to buy mine from, so now I'm basically forced to use KDP's free ISBNs by default.

Here's the catch with that. Outside of KDP's Expanded Distribution, if I want to sell my books anywhere other than through KDP itself, I have to get a separate ISBN for each additional place I sell.

The tradeoff

Why does one free number cost you flexibility later? Because a platform-provided ISBN, like KDP's free one, makes that platform the “publisher of record” for your book. That's fine if you're genuinely happy publishing through just that one platform. But it's real friction if you ever want to expand: getting into other stores or platforms without picking up more ISBNs along the way is genuinely harder.

A self-purchased ISBN, through a service like Bowker here in the US, flips that tradeoff. It costs more upfront, but it's portable. You own it outright, and you can use it anywhere, on any platform, for this book or for whatever you write next.

So the real question isn't “which ISBN is better,” it's which tradeoff you'd rather make: pay nothing now and stay tied to one platform, or pay upfront and keep the freedom to go wherever you want later.