File extension

.epub

EPUB electronic publication

.epub files are EPUB e-books: an open e-book standard that packages reflowable XHTML content, CSS, and media as a ZIP archive, readable across a wide range of e-reading devices and apps.

Known meanings

Formats and reference material for .epub

EPUB electronic publication

Open, ZIP-packaged reflowable e-book format based on XHTML and CSS

  • documents internet
  • W3C (formerly IDPF)
Open link

Details

Format notes

EPUB

EPUB is the leading open standard for digital books, maintained today by the W3C (originally by the International Digital Publishing Forum). Its defining strength is reflowable content: rather than fixing text to a page like a PDF, an EPUB lets the reading system adapt the layout to the screen size, font, and user preferences, which is why it is the format of choice for novels and other text-centric books on phones, tablets, and dedicated e-readers.

Under the hood, an EPUB is essentially a website packaged as a ZIP archive. The content is authored in XHTML and styled with CSS, with images, fonts, and media included as separate files. A META-INF/container.xml points to a package document (the OPF file) that lists all the resources (the “manifest”), defines the reading order (the “spine”), and carries metadata such as title, author, and identifier; a navigation document provides the table of contents. The ZIP must store its first entry, mimetype, uncompressed so the format can be identified quickly.

Versions And Fixed Layout

EPUB 3, the current generation, is built on modern HTML and CSS and supports rich media, scripting, accessibility features, and MathML, while remaining backward-aware of the older EPUB 2. A “fixed-layout” profile exists for content like children’s books and comics where precise page design matters more than reflow.

Preservation And Security Notes

EPUB is well suited to preservation because it is open, standards-based, and built from documented web technologies; note that commercially distributed e-books may be wrapped in DRM, which is a separate access barrier from the format itself. As ZIP-plus-web-content, reading systems should apply archive precautions and treat embedded scripts and external references as untrusted. The media type is application/epub+zip.

Further Reading

  • EPUB 3 specification (W3C): https://www.w3.org/publishing/epub3/