Short for electronic publication, EPUB is the most widely supported open, free e-book format, with popular e-book readers like Barnes and Noble’s Nook, Apple iOS-powered devices such as the iPad and iPhone, the Sony Reader and more supporting the standard. Of the major e-book readers on the market today, only Amazon’s Kindle lacks built-in support for the EPUB format.
Currently in version 3.0, the EPUB standard was originally created by the International Digital Publishing Forum (IDPF) in 2007. In addition to EPUB being supported by most popular e-book readers, the format can also be read on Android devices via apps like Moon+ Reader and WordPlayer, Windows Phone 7 via apps like Freda, and Mozilla Firefox via browser add-ons like EPUBReader and Okular. EPUB files use the .epub file extension.