ISBNs are the global book identifier
The International Standard Book Number (ISBN) is a numeric commercial identifier designed to be unique for books. Publishers obtain ISBNs through national agencies that operate under the International ISBN Agency.
Retail systems, libraries, and distribution partners use the ISBN as the primary key to track, order, and report on book sales.
Every edition and format needs its own ISBN
A separate ISBN is assigned to each edition and variation of a publication. That means paperback, hardcover, and ebook versions of the same title each carry their own ISBN.
This separation keeps catalogs clean and prevents sales data for different formats from being blended together.
ISBNs switched to 13 digits in 2007
ISBNs assigned before 2007 are 10 digits, while ISBNs assigned on or after 1 January 2007 are 13 digits. This shift aligned ISBNs with global barcode systems.
For modern distribution, 13-digit ISBNs are now the default across retailers and libraries.
Bookland prefixes connect ISBNs to barcodes
The prefixes 978 and 979 were introduced to let ISBNs fit into the EAN barcode system used for retail scanning.
This lets books live inside the same global product catalog used by retailers without needing a separate barcode standard.