From early 2020 the United States ISBN Agency (operated by Bowker) will begin assigning ISBNs starting with the prefix element 979. (These assignments will be in addition to  ISBNs with prefix element 978 that the US currently assigns). The introduction of ISBNs from the 979 ranges is necessary to increase the available inventory of some ISBN block sizes.

What does this mean for publishers, libraries and retailers?
Prior to 2007, the ISBN was 10 digits in length. In January 2007, the 13-digit ISBN was launched to increase the capacity of the ISBN system.

Currently, all 13-digit ISBNs assigned by the US ISBN Agency use the 978 prefix, which allows systems to contain both 10- and 13-digit ISBNs for all books.

However, a 13-digit ISBN starting 979 is not backwards compatible and does not have an equivalent 10-digit ISBN. Trying to convert a 979 ISBN into a 10 digit ISBN will bring serious errors including duplicated ISBNs and incorrect supply of orders. All ISBNs must be recorded in all systems and communicated to partners ONLY in their complete 13-digit form.

Bowker will continue to assign ISBN blocks starting with 978 until their inventory of a specific block size has been exhausted and is replaced with 979. This means that for some time the US ISBN Agency will be issuing ISBN blocks that originate from ranges that may come from under 978-0, 978-1 or 979-8. It is vital that ISBNs are recorded and transmitted accurately in their complete 13-digit forms.

Changes to country classifications
Currently, the US ISBN Agency assigns ISBNs starting with either 978-0 or 978-1. 978-0 and 978-1 indicate assignment by an ISBN Agency in an English-speaking region.

979-8 will be unique to the United States and its associated territories (e.g. American Samoa). Of course, as with the 978-0 and 978-1, an ISBN starting with 979-8 will allow US publishers and self-publishers to identify, market and sell their books anywhere in the world.