Do I have to have an ISBN to list my title on NetGalley?

No. You can come up with a 13-digit number on your own if you so choose. There are random-number generators available on the internet. The number just has to be unique to NetGalley. NOTE: If you do not use an ISBN, some of NetGalley's features that rely on this unique identifier will not work correctly, specifically retailer links to your title.