Amazon Kindle Format or Mobipocket Format: These files have a .azw or .mobi extension and can only be used on Amazon Kindle devices.
E-pub: These files have the .epub extension and can be used on a variety of devices (e.g. Barnes and Noble Nook, Sony eReader, Apple iPhone/iPad, etc).
E-pub files are available via direct download from Crossway.org or an eBooks store like the Barnes and Noble eBook Store, Sony eBook Store, or the Apple iBook store.
Since many eReader manufacturers support e-pub format and have specific procedures for loading e-book files, we recommend you consult the instruction manual for your specific device. Generally, connecting an eReader device to a computer via USB and copying the e-pub file into the correct folder of the device should be all that’s required.