All of my books have disappeared. How do I get them back?

Had you synced to your computer's iTunes ? If you synced to your computer and the books aren't on your computer's iTunes then that might have removed them.

If they are ibooks purchases then you should be able to use the Store button at the top left of the bookshelf to go into the ibookstore in the app and re-download them via the Purchased tab at the bottom of the store. You can then connect to your computer and copy them over to your computer's iTunes via File > Transfer Purchases so that you have a copy of them for backing up/re-syncing purposes

I have lost most of my books that i transferred from my samsung which i gave to my sister.

I cant get my books back with no help from apple

very disappointing a major flaw with ipad and no solution.

I have taken my iPad back to factory settings and restored but still the books are not there

Books are not included in a backup, neither iCloud nor iTunes. Have you got the in the Books part of your computer's iTunes library - prior to removing them from your iPad did you copy them over (File > Devices > Transfer Purchases should have copied them over from the iBooks app even if they weren't iTunes purchases) ? If not then you will have to recopy them where they originally came from

to king penguin

the books disappeared before I ever did a backup

it was obviously an error in the iPad operating system.

all these books I paid before I moved over to apple Ipad,I had about 2000 books

sorry what I meant to say was that the books disappeared long before I ever did a compete restore

The contents of the iBooks app are not included in a backup, an iTunes restore would look for them in the Books part of your iTunes library (or iBooks app if using a Mac with Mavericks or Yosemite on it), an iCloud restore will redownload your iTunes purchases that it can.

Had you ever done File > Devices > Transfer Purchases to copy them over to your computer's iTunes library (and if using a Mac then done File > Move Books From iTunes in its iBooks app) ? That should have copied epubs and/or PDFs that werein the iBooks app, not just actual ibooks. If you had then you should be ableto sync them back.

What had you done with the iPad prior to them disappearing ? If you had synced the iPad to your computer when they were not in the Books part of your computer's iTunes library, then you may have effectively told iTunes to replace the current contents of the iBooks app with your selection in iTunes.

If you have copies of them anywhere on your computer then you can add them to your computer's iTunes library via File > Add To Library (or to the iBooks app if using an up-to-date Mac) and sync them back to your iPad