An EPUB file is an e-book file format that uses the ".epub" file extension. It is a standard that supports a variety of eBook hardware and software. EPUB is supported by many e-readers, and compatible software is available for most smartphones, tablets, and computers. EPUB is a technical standard published by the International Digital Publishing Forum (IDPF) and became an official standard of the IDPF in September 2007, superseding the older Open eBook (OEB) standard. The Book Industry Study Group endorses EPUB 3 as the format of choice for packaging content and has stated that the global book publishing industry should rally around a single standard.

EPUB files can store words, images, stylesheets, fonts, metadata details, and tables of content. They are considered layout agnostic, meaning that screen size doesnt affect the formatting, and EPUB files can display content on screens as small as 3.5 inches. The EPUB format is implemented as an archive file consisting of XHTML files carrying the content, along with images and other supporting files. EPUBs are the most popular file format extension used for the storage of eBooks and other related content.

EPUB is the most widely supported vendor-independent XML-based e-book format, and it is supported by almost all hardware readers. However, the notable exception is Kindle, which uses a proprietary file format, and you cannot read an EPUB file directly on a Kindle. But there are ways to convert an EPUB file to something the Kindle can use.

EPUB files are primarily used in the viewing of eBooks, and you can download and open them on eReaders such as Adobe Digital Editions (ADE), as well as smartphones, tablets, or computers. The latest version, EPUB 3.2, supports HTML, CSS, and SVG, with built-in support for video, audio, and even interactive features.