.epub File — Electronic Publication

EPUB is the most widely supported open standard for digital books and publications, maintained by the W3C. An EPUB file is a ZIP archive containing XHTML content files, CSS stylesheets, images, fonts, and an OPF package file that describes the book's metadata, manifest, and reading order. EPUB 3, the current version, supports rich media, JavaScript interactivity, MathML for mathematical equations, SVG graphics, and advanced CSS layout including pagination and multi-column text. Unlike fixed-layout formats like PDF, EPUB is primarily a reflowable format that adapts content to different screen sizes and allows readers to adjust font sizes and styles. EPUB supports accessibility features including semantic markup, ARIA attributes, and text-to-speech synchronization through SMIL media overlays. The format is used by most major e-book retailers and libraries except Amazon, which uses its proprietary Kindle formats. EPUB is the recommended format for digital publishing by numerous international standards organizations.