EPUB® defines a distribution and interchange format for digital publications and documents. The EPUB format provides a means of representing, packaging and encoding structured and semantically enhanced Web content—including HTML, CSS, SVG and other resources—for distribution in a single-file container.

About EPUB 3.3

EPUB 3.3 is a revision of the EPUB 3 specification, which can be considered as a successor to EPUB 3.2. It is also the first W3C Recommendation of the EPUB series of specifications.

EPUB 3.3 is backward compatible with EPUB 3.2, insofar as any EPUB 3.2 document is also valid EPUB 3.3. In other words, moving from EPUB 3.2 to EPUB 3.3 does not require any changes to current publication workflows.

The W3C process of standardization entails a thorough review of the specifications by Member experts, including checking the specification’s impact on implementations for internationalization, security, privacy, accessibility, and conformity to other Web standards. These reviews led to a number of small but important technical changes such as additional features to address bidirectional text, and more precise specification of security related details for scripts. The standard also includes detailed guidelines for implementers on the possible privacy and security problems.

The Working Group has also created a comprehensive test suite that systematically tests all normative features of the specification.

EPUB 3 documents


EPUB 3 is currently defined by the following specifications:

The recommendation-track documents include detailed change logs on the substantive changes since the previous official releases. See the change log for EPUB 3.3, EPUB reading systems 3.3, and EPUB Accessibility 1.1, respectively.


Although the following documents are informative, they provide guidance related to implementing the EPUB 3 specifications as well as define experimental features.

How to Participate

The EPUB 3.3 specification is developed by the W3C EPUB 3 Working Group and is now maintained by the Publishing Maintenance Working Group. All Working Group activities are conducted in an "open source" manner: the EPUB 3 specifications' site is publicly accessible.

All comments on EPUB 3 specifications should be submitted via the EPUB 3 issue tracker hosted on GitHub. (NOTE: you must login via a GitHub Account in order to submit an issue.)