Why are there so many version listings for some books? Example: Heartbreaker by Joy Fielding. There seems to be about 6 different ISBN's listed. How does that happen??? I thought each title only gone one number. Thanks for any info or comments.

No, each edition from each publisher can get a different ISBN number.  In general, each different publisher will get a differernt ISBN number.  Heck, if a publisher wants to spend the money, they could issue the same edition and title under multiple ISBNs.

In general, the older and more popular a title, the more ISBNs may be associated with it.

Some are paperback, some hardback some audio. And there are sometimes more than kind of each, so a different isbn for each one.

It will say in the discription what version it is.

Also diff numbers in Canada/Britain/Australia, etc.

You have ISBNs for mass market paperback, trade size paperback, hardcover, audio cassette, audio CD, and for different publishing years if the book has been re-published. 

I must be bored because I actually looked this up.  Assuming that the O.P. meant to refer to Heartstopper, here's what I found listed:

• One hardcover by Atria with 368 pages
• One hardcover by Atria with 496 pages - presumably the large print version
• One hardcover by Doubleday Canada
• One paperback version by Pocket with 592 pages (the ISBN starts with a 1 which usually means it was printed in a country other than the U.S.)
• One paperback version by Pocket with 368 pages (the difference in the pages is confusing - probably this is a trade paperback version))
• One hardcover that was posted to the system by a member as a book without an ISBN - either the member was confused or perhaps the book was a book club printing?
• One audio CD listing for libraries
• One audio CD for non-libraries.

So it looks to me like these are all significantly different version.

I thought each title only got one number (changed gone to got, as I assumed that's what you meant)

If you mean here on PBS, it's each number only gets one BINDING. As you've seen from the responses above, each title can have many numbers given for various reasons. But, when posting a title, you have to double check the number, because it may be different than the one already posted, OR it may be the same but a different BINDING and then you would have to post it as tho it did not have one, using the non-ISBN posting page.