EPUB 3 vs EPUB 2: What's the Difference and Why It Matters
EPUB 3 is the current standard. EPUB 2 is obsolete but still widely encountered. Understanding the difference matters if you're publishing, distributing, or validating ebooks — or converting PDFs to EPUB.
The short version
- EPUB 2 — 2007 standard, HTML 4/XHTML 1.1, limited accessibility, no multimedia, NCX navigation
- EPUB 3 — 2011+ standard (latest: EPUB 3.3, 2023), HTML5, MathML, SVG, multimedia, WCAG accessibility, NAV document
- EPUB 3.x is what you should produce today. EPUB 2 is deprecated by the W3C.
What changed in EPUB 3
HTML5 content documents
EPUB 2 used XHTML 1.1 — no <article>, <section>, <nav>, or semantic elements. EPUB 3 uses HTML5, which enables proper document structure that screen readers and accessibility tools understand.
Accessibility (EPUB Accessibility 1.1)
EPUB 3 introduced epub:type semantic inflection and later role attributes aligned with ARIA. The EPUB Accessibility 1.1 specification (built on WCAG 2.x) only applies to EPUB 3. EPUB 2 has no formal accessibility conformance path.
This is critical for the European Accessibility Act (2026) and Section 508 compliance — both require WCAG 2.x conformance, which only EPUB 3 can formally satisfy. EAA compliance guide →
Navigation document
EPUB 2 used an NCX (Navigation Control for XML) file. EPUB 3 replaced this with a proper HTML5 NAV document — a real web page that e-readers and screen readers navigate identically. EPUB 3 files can include an NCX for backwards compatibility with older reading systems.
MathML and SVG
EPUB 3 supports MathML directly in content documents — essential for scientific and mathematical texts. EPUB 2 rendered equations as images. SVG is also a first-class spine item in EPUB 3.
Media overlays (read-aloud)
EPUB 3 supports synchronized text-audio media overlays (SMIL), enabling "read aloud" synchronized highlighting. Useful for educational and accessibility-focused publications.
Scripting
EPUB 3 allows JavaScript in reading systems that support scripting. EPUB 2 did not. In practice, scripting support varies across e-readers — most reflowable fiction/non-fiction EPUBs don't use it.
Device compatibility
All modern e-readers and apps support EPUB 3:
- Kindle (via Send to Kindle, Kindle app, or USB) — EPUB 3 reflowable
- Kobo — full EPUB 3 support including fixed layout
- Apple Books — full EPUB 3 including media overlays
- Thorium Reader — full EPUB 3 including accessibility features
- Google Play Books — EPUB 3 reflowable
Older Kindle firmware (pre-2022) had limited EPUB support. Current Kindle firmware handles EPUB 3 reflowable content well.
What toolkit.bot produces
All conversions produce valid EPUB 3.x output — HTML5 content documents, a NAV navigation document, EPUB Accessibility 1.1 metadata targeting WCAG 2.2 AA structural requirements. EPUBCheck validates the output as EPUB 3.
When would you still encounter EPUB 2?
- Old ebooks downloaded before 2015 from Project Gutenberg or similar
- Legacy publishing workflows that haven't updated their toolchain
- Some older Calibre conversions (Calibre still defaults to EPUB 2 for some source formats)
EPUB 2 files open fine in modern readers — backwards compatibility is maintained. But if you're producing new EPUBs, always produce EPUB 3.
Convert your PDF to EPUB 3 — valid, accessible, free.
Convert PDF to EPUB →