Do I need an ISBN to publish on Smashwords?

If you plan to publish only on Smashwords' Standard Catalogue, you will not need an ISBN. If you plan to publish in Smashwords' Premium Catalogue and you would like them to distribute your ebook to Kobo and Apple, you will require an ISBN.

You can assign your ISBN to your ebook in your Smashwords Dashboard, through the ISBN Manager. 

For more information regarding ISBNs and publishing on Smashwords, click here.