EPUB goes back further than you might expect: its roots lie in OEBPS (Open eBook Publication Structure), an interchange format approved in 1999. The body that drafted it was later organised as the International Digital Publishing Forum (IDPF).
It then became clear that a format able to bundle everything into a single distributable file was needed, and EPUB 2.0 was approved in October 2007. In September 2010, EPUB 2.0.1 was published, mainly to clarify the specification and correct errors.
Then in 2011 came the major revision, EPUB 3.0. It tied the format closely to HTML and brought multimedia, refined layout and font embedding, scripted interactivity, stronger global language support and better accessibility. Media Overlays — the specification for synchronising text with audio — was introduced at the same time.
So EPUB 3.0 was not merely a version bump; it was the edition that rebuilt the foundations of the format.
From a maker’s point of view, these are the differences that matter.
| Item | EPUB 2 | EPUB 3 |
|---|---|---|
| How the text is written | XHTML 1.1 as the base | Based on HTML5 |
| Table of contents | toc.ncx | A navigation document (nav.xhtml) is mandatory |
| Japanese vertical text | Effectively impossible | Supported |
| Ruby | Effectively impossible | Supported |
| Fixed layout | None | Supported |
| Sync with audio | None | Media Overlays |
The one with the biggest day-to-day impact is how the table of contents works. The file EPUB 2 used, toc.ncx , was replaced in EPUB 3 by the new navigation document. In EPUB 2 reading systems, support for toc.ncx was optional; in EPUB 3 it is mandatory both to include a navigation document and to support it.
Look inside an EPUB and you may find both nav.xhtml and toc.ncx . That is a courtesy so that older reading apps still get a table of contents. As EPUB 3, nav.xhtml alone is enough, but the old file is sometimes kept for compatibility.
This is the most important point for anyone making books in Japan.
Japanese vertical text and ruby became usable with EPUB 3. In the EPUB 2 era it was effectively impossible to express a Japanese book in the standard. As a result, ebooks in Japan ran for years on proprietary per-company formats.
That changed partly through effort from the Japanese side. According to the Japan Electronic Publishing Association (JEPA), from 3.0 onward, through considerable effort and advocacy by Japanese experts and stakeholders, Japanese requirements were substantially incorporated, and EPUB’s position as the ebook format in Japan became unshakeable.
The same explanation notes what becoming a standard meant: anyone can now produce ebooks freely, for the great majority of readers. That, it argues, is EPUB’s greatest advantage.
In other words, an individual can put their own novel out as a vertically set ebook because EPUB 3 exists. That one line about "stronger global language support" carries this much weight for a Japanese speaker.
The specification has kept being updated since EPUB 3.0.
| Edition | When | Where it sits |
|---|---|---|
| EPUB 3.0 | 2011 | Major revision of EPUB 2. Vertical text, ruby and fixed layout |
| EPUB 3.0.1 | 2014 | Maintenance and improvement |
| EPUB 3.1 | 2017 | The last edition under IDPF |
| EPUB 3.2 | May 2019 | Drafted by the W3C EPUB 3 Community Group. Compatibility-focused |
| EPUB 3.3 | May 2023 | First W3C Recommendation in the EPUB series |
| EPUB 3.4 | In progress | Candidate Recommendation July 2026. Recommendation expected on or after 19 October 2026 |
When IDPF merged into W3C in 2017, the EPUB specification came under the body that sets web standards. That history is why EPUB 3.3 is called "the first W3C Recommendation".
The editions are built to stay compatible. EPUB 3.3 is backwards compatible with EPUB 3.2: a file that is valid as EPUB 3.2 is valid as EPUB 3.3. Moving from 3.2 to 3.3 was stated to require no change to how you produce books.
The next edition, EPUB 3.4, is looking at dark-mode support and standardising how footnotes and endnotes are written. There is also a dedicated team looking at digital comics, so the open questions about handling manga in EPUB are being argued out internationally right now.
One question follows from all of this. If the current edition is 3.3, why do so many tools and stores say "supports EPUB 3.0"?
The answer is simple: the format name "EPUB 3" is being confused with the version number of the specification.
W3C’s own explanation lists this as a common stumbling block for newcomers. It states plainly that the decimal numbers distinguish releases of the specification, and a new edition does not mean a new format.
So "supports EPUB 3.0" is, strictly speaking, almost always being used to mean "supports the EPUB 3 format". There is no need to build different files for 3.0 and 3.3.
The conclusion for a maker is simple.
nav.xhtml for the table of contents. Add toc.ncx alongside it if you want to be kind to older environmentsIn practice, a tool that generates EPUB for you satisfies these requirements on your behalf. There is almost never an occasion to worry about version numbers by hand.
Pick a folder of images or a text manuscript and you get an EPUB 3 ebook file. No account, no installation.
Try EPUB FACTORY