We buy the International Standard Book Number so that it can be recognized by any database anywhere in the world. They are allocated to publishers, and identifiable as such, so they cannot be transferred between individuals/companies or titles. They are 13 digits – prior to 2007 they were 10 digits, so for some books we have two. A separate ISBN is not necessary for Amazon, but it is for most other online outlets. You can find the paperback ISBN in the top left-hand corner of your Book Details page; it is also listed at the bottom of your Book Details page under META DATA, as is the ebook ISBN.
We sometimes re-package titles, particularly if an author has published several with us, they're going well, and we want a more consistent approach for them. In which case-
The ISBN Agency says publishers need to assign a new ISBN if
And publishers don’t need to assign new ISBN if