The two most popular ebook formats used by publishers and online retailers are ePub and Mobi. Because some retailers carry only ePub ebooks and others carry only Mobi, most publisher will publish two ebook editions, one for ePub and one for Mobi. Both of these formats offer essentially the same appearance and functionality.
Both formats allow the book page to take the shape and size of whatever screen they are displayed on. Likewise the type can be scaled by the reader to suit personal preferences. These two features enable ePubs and Mobis to be read confortably on numerous devices including cell phones.
Fonts can also be controlled by the reader on some devices. The ePub and Mobi formats allow hyperlinks and the table of contents is usually linked to the chapters.