The latest version of the EPUB format, EPUB 3.3, is now a W3C standard, and was officially published as Recommendation on 25 May 2025. EPUB 3.3 has in fact successfully passed the standardization process defined by the W3C, which allows technical reports, after repeated rounds of reviews by expert Members and after demonstrating the specification’s effective implementability, to leave the Candidate Recommendation stage and become a fully-fledged standard.

The EPUB Accessibility 1.1, of which Gregorio Pellegrino (Chief Accessibility Officer of LIA) is co-editor, have also become a standard. The document represents an update of the guidelines for the accessibility of EPUB publications.

Accessibility has been a key point in the drafting of the new EPUB 3.3 specification. For the first time in the format’s history, EPUB Accessibility is now an integral part of the EPUB standard.

Moreover, the guidelines have been updated to ensure the compliance of EPUB publications with the requirements of the European Accessibility Act. For these reasons, Fondazione LIA is already adjusting its certification process to align with this new version of EPUB Accessibility and ensure that all publications certified as accessible are compliant with the current regulations.

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In addition to the integration of EPUB Accessibility 1.1 into the EPUB 3.3 specification, there are two other key aspects to note: the reorganization of the specification documents and the development of a test suite.

The EPUB Reading System 3.3 specification, which defines the requirements for rendering EPUB publications in reading systems, is now a separate document, whereas in version 3.2 the same document contained both the instructions for the creation of EPUB content by publishers and content creators, and the requirements for EPUB reading systems, intended for developers of such systems. In addition, poorly adopted features, such as multiple renditions, have been removed from the main document and published separately.

The structure of the specification itself has therefore been changed with the aim of making it easier to consult and understand.

The test suite, on the other hand, represents a collection of EPUB files that can be used to systematically test reading systems against all normative features of the specification of the format itself and the EPUB Reading System 3.3. Each file allows a specific functionality to be assessed, such as the support for different image formats (JPEG, PNG, SVG, WEPB) or handling links to external resources in the EPUB file. The suite was developed to help make EPUB publications increasingly interoperable between different reading solutions.

What changes for publishers?

EPUB 3.3 is compatible with the previous version, for EPUBs already valid for 3.2. The latest version of EPUBCheck (5.0.1) is also fully compatible with EPUB 3.3: the transition to EPUB 3.3 therefore does not require any changes to the current publication flows.

The W3C announced the publication of the Recommendation with an official press release.