If you are planning to self publish your book through BookBaby, the answer is yes. Your ISBN is how we identify your book within our systems and ensure we are crediting all of your online sales to the correct account.
You can supply your own ISBN purchased through Bowker or another ISBN issuing agency from outside of the US. If you do not have an ISBN, BookBaby can assign you a number for each version of your book (eBook, printed book) for $29. You will need a separate ISBN for each format of your book – one for your eBook and another for your printed book.
If you are selling your printed book on your own (direct to reader sales from your website, bookshows or book signings, etc.) you are not required to have an ISBN. However if you wish to have any other type of distribution through online retailers (except for Amazon), distributors or other catalogs, an ISBN is required.
If you live outside of the USA, you may purchase an ISBN through BookBaby. Some countries provide free ISBNs. Contact your local ISBN issuing agency for information on how to obtain an ISBN in your country.