ePubs

EPUB, short for electronic publication, is an open e-book standard designed for reflowable digital publications such as novels, magazines, and textbooks. It is the most widely supported format for e-books and is intended to be platform-agnostic and accessible across devices and apps.

A typical EPUB file is a ZIP archive that contains HTML or XHTML content, CSS styles, images and fonts, and a set of metadata files. The central package document, called content.opf, describes the document’s metadata, manifest, spine, and guide. EPUB 2 used a separate table of contents file (toc.ncx); EPUB 3 uses a semantic navigation document in HTML5.

EPUB was originally developed by the International Digital Publishing Forum (IDPF). In 2016-2017 the IDPF work was brought under the umbrella of the World Wide Web Consortium (W3C). The most widely used version today is EPUB 3.x, with several updates that improve HTML5 support and accessibility.

EPUB supports reflowable text, allowing readers to adjust font size, margins, and layout. It also supports fixed-layout formats for heavily illustrated works, multimedia, and complex layouts. EPUB files may include interactivity, embedded fonts, multimedia overlays for read-aloud features, and accessibility metadata to aid screen readers.

While EPUB is an open standard, some reading ecosystems apply digital rights management or conversion requirements, and not all devices natively support EPUB. Tools exist to create, validate, and convert EPUB files, and publishers frequently distribute EPUBs to major storefronts such as Apple Books and Kobo.