Many self-publishing platforms, such as CreateSpace and Smashwords, offer free ISBN numbers to customers who publish through their imprint. A free ISBN number often comes with restrictions on the marketing and distribution of the book, however.
Bowker is the official ISBN issuing agency for the United States. An ISBN number purchased through Bowker may offer additional advantages over a free ISBN number, including the ability to select the publisher name. Many self-publishers offer customized ISBN numbers that are not free but may be more cost-effective than the Bowker option. Free ISBN numbers are often designed to work well within a particular publishing platform and may restrict other avenues of distribution.