epub

EPUB, short for electronic publication, is an open standard for distributing and presenting digital publications and documents, including e-books. It is designed to support reflowable text that adapts to different screen sizes, as well as fixed-layout content for magazines or comics. The format was originally developed by the International Digital Publishing Forum (IDPF); after its merger into the W3C, EPUB specifications continued under the W3C framework.

An EPUB file is a ZIP archive with a .epub extension. Inside it are content documents in XHTML or XML, CSS styles, images, and metadata. The Open Packaging Format (OPF) defines the manifest of resources and the reading order, while a navigation document provides the table of contents. EPUB 3.0+ adds support for HTML5, CSS3, multimedia, interactivity, embedded fonts, accessibility features, and SVG/MathML as needed. Fixed-layout EPUBs preserve page designs for certain genres.

Common features include metadata, reflowable text, support for multiple languages, and media overlays for synchronized read-aloud narration. EPUB is designed to be device-agnostic and platform-neutral, enabling broad interoperability across readers and apps. DRM is not part of the EPUB specification itself but many distributors implement proprietary digital rights management.

EPUB is the most widely used open e-book format and remains a standard for electronic publishing, competing with proprietary formats such as Kindle's MOBI/AZW. It remains under active development to improve accessibility and support for contemporary web standards.