epub The ePub format is one of the many open source eBook file formats available. Initially released in 2007, it succeeded the legacy Open eBook format. The format was first defined by the Open eBook forum, part of the international digital publishing forum. EPUB digital books and publications all have the associated .epub extension and can be opened and viewed on any compatible device, software application, smartphone, or dedicated reader. The format is capable of optimizing the resolution of digital publications to suite the resolution of the device being used, making it inherently a 'reflowable' format.
mobi The .mobi filename extension is an eBook file format developed by French company MobiPocket for their ebook readers for mobile phones and PDAs. The company was later acquired by book reseller and online store company Amazon in 2005, a deal which included the mobi format asset. The mobi file format is mostly associated with the mobipocket software package as well as early versions of Amazon's kindle ebook reader device. The format is considered cross platform given its compatibility with several devices including most smartphones that have compatible readers installed. But although mobi files still exist in circulation, the format was superseded by Amazon's AZW format when support and further development of mobi ceased in 2011.