# What is EPUB 3?

Source: https://epublab.com/glossary/epub-3/ (updated 2026-11-03)

EPUB 3 is the current version of the EPUB e-book standard, built on XHTML5, CSS, SVG and an HTML navigation document. Its latest revision, EPUB 3.3, became a W3C Recommendation in 2023.

## Why it matters when you convert a PDF to EPUB

EPUB 3 is the format to produce today: it supports semantic markup for footnotes (epub:type), right-to-left and vertical writing, MathML, accessibility metadata and page lists that map back to the printed pages of the PDF. EPUBLab writes EPUB 3 and validates its benchmark output with EPUBCheck.

An EPUB 3 file can also carry an NCX table of contents so that very old EPUB 2 reading systems can still navigate it. Validators check EPUB 3 files against the EPUB 3.3 rules.