File with a .MOBI extension contains an eBook and information on its copyrights, access permissions and DRM copying. This format war created in the year 2000 for use of French Mobipocket Reader devices, and since the year 2005, it is accepted and developed by Amazon company. An alternative for the MOBI files are the PRC files, while the opened analogue equivalent is EPUB. They can be created within Amazon for Windows software or Mac OS KindleGen and they can opened with Kindle Previewer.

Formats of Amazon Kindle eBooks, such as AZW, AZW1 and AZW3, are based on MOBI, but they introduce proprietary DRM information and advanced formatting options, such as fonts, HTML 5 functions and CSS3. Files in the above mentioned KF8 format can be stored with the .MOBI or .AZW3 extensions, therefore, not every eBook reading device, a tablet or PDA or a PC applications which support the older MOBI files, will be able to read them according to the latest Amazon specification.