Every country has its own "clearinghouse" that handles ISBN numbers for that country. In the US, that is at Bowker.com. The fees add up to about $30/ISBN. Bowker tries to get you to buy in blocks of ten - but you can actually get just one if you want, for $125. For this reason, if you don't need ten, it might be worth it to talk to some friends and get ten as a group. There is also a "black market" on the web where you buy unused numbers from other people who bought a set of ten.
Once you get your Bowker ISBN numbers, it's a good idea to let Bowker know when you assign a title to each one. They maintain a master database that many other companies access. You update this information at BowkerLink
In any case, if you want to buy from Bowker directly as a legitimate purchase, you can do pretty much the entire process online and charge it to a credit card.
Again, you don't NEED an ISBN number to publish a book or ebook on your own, personal website. However, if you want Amazon and most other bookstores to carry your book, then they will require an ISBN number as part of their tracking system.
This becomes even worse when you look at ebooks. Many ebook sellers claim that their ebook format is enough different from other ebook formats that it requires its own ISBN. So the Kindle ISBN is different from a SmashWords ISBN which is different from an iTunes ISBN and so on. You can see how this can rack up your costs very quickly.
This is why it's wise to consider simply using free ISBN numbers.
Free ISBN Numbers
I used to recommend you buy your own ISBNs directly from Bowker and control them all personally. I liked the idea of controlling exactly what was listed in the Bowker master database. I've long since given up on that theory. It would cost thousands of dollars and, really, it brings practically zero benefit in our modern world. Nobody ever looks at Bowker for book information. They look at Amazon, or Barnes & Noble, or whatever other system they're using.
Now I just allow each organization - CreateSpace for print, Kindle for Amazon ebooks, Smashwords for the Smashwords site, Kobo for the Kobo site, and so on, to assign a free ISBN for their system. Yes, it means they get credit for "publishing" your book on their platform. It really doesn't matter at all. You're in their system, you own fully copyright to your book, and you get all proceeds. It just boosts their "marketing numbers" when they can claim that they've published X million books in the past month.
THEY DO NOT TAKE YOUR COPYRIGHT. The one and only thing this impacts is the name of the "publisher" in the Bowker record. You can still have your own imprint name, if you wish. For example, my books are all published as part of the Minerva Webworks LLC publishing system. I can still put that on each book.
You get that ISBN free as part of the process of entering the book into their system. Then simply include that ISBN number on your copyright page.
Bar Code Version of your ISBN
It's traditional, on the back cover of a print book, to have a bar code version of your ISBN number shown. This is nothing special and should not cost ANY money. This is simply a bar code which shows the ISBN number. Bar code is a standard "language" of thick and thin lines. You can download a bar code as a font or get free bar codes from many different websites. They just need to be in EAN-13 format. You should never have to pay to get a bar code, if you want to put it on the back of your print copy cover. Most publishers will do this step for you for free.
Amazon also has an internal tracking number they use for their Amazon Kindle Ebooks, called an ASIN. This is an Amazon-specific ID number they assign to each ebook. They assign this automatically and the process is free.
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