Direct answer
KDP can provide a free ISBN for eligible paperback and hardcover books, but Amazon says that free ISBN can only be used on KDP. Buying your own ISBN gives you an identifier you can use with other publishing services, provided the metadata is registered correctly.
When a free KDP ISBN may suit
It can simplify a KDP-only print release where the author does not need to use the same ISBN through another publishing service.
When your own ISBN may suit
Authors planning broader distribution or who want control of the registered imprint often prefer to obtain their own ISBN from the official agency.
Each format is separate
Paperback and hardcover editions require separate ISBNs. KDP says ebooks do not require an ISBN.
Official sources
Platform fees and rules can change. Use the source links below when making a final publishing decision.
This page provides general publishing information, not legal, tax or financial advice. Service scope and third-party platform terms should be confirmed before purchase or publication.
