title_body: How do I get an ISBN? Given that it is not necessary to have an ISBN if you plan to self-publish an ebook only via Amazon (they use their ASIN), which is the best way to get one, if someone plans to sell his/her book also in epub (or pdf) format?
  
  I know that there national official bodies which manage ISBN space: for example Bowker for the US and isbn.it for Italy; and there are "sublicensers" which are a bit cheaper. But there are also firms which give you a ISBN for your book, but remain officially the publisher for the book. Which are advantages and disadvantages for these options?
upvoted_answer: The national official bodies that you mention are the only ways to get an ISBN in your name for your manuscript. If you go through, say, Smashwords to get your ISBN, then Smashwords will be on file at the ISBN agency as the publisher of the manuscript. When you get an ISBN from anywhere else, they are basically buying them from Bowker (or whoever) in bulk and reselling them for a markup. Here's some further info: https://savvybookwriters.wordpress.com/2012/06/08/author-beware-unauthorized-resellers-of-isbns/