EPUB3 Explained: Features, Compatibility, Best Practices

EPUB3 makes ebooks more structured and consistent in navigation, with cleaner HTML/CSS output when converted well.

It is the current W3C standard, and it is backward compatible with EPUB 3.2—so most workflows don’t need changes to move forward.

The enemy of compatibility is complex CSS, excessive fonts, and fixed layout when you don’t need it.

If you must support very old devices, EPUB2 can still be useful—but it is legacy and not actively maintained.

EPUB3 aligns with modern accessibility guidance and supports richer metadata for discoverability.

In practice, accessibility still depends on the quality of your source: headings, reading order, and language metadata are the biggest wins.

Keep EPUBs simple and semantic for best results.

Use EPUB 3.3 as the default for new work. Its navigation document is mandatory and must contain one table-of-contents navigation element, giving reading systems a predictable, machine-readable way to expose the book's structure.

Compatibility depends less on the version number than on disciplined authoring. Prefer semantic XHTML, relative units, flexible images, a small stylesheet, and system fonts unless the publication genuinely depends on a licensed embedded typeface.

Separate essential content from enhancements. A reader that ignores scripting, media, or advanced styling must still expose the complete text, usable navigation, and a sensible reading order. Test those essentials with EPUBCheck and at least two reading systems.

Gate one is conformance: EPUBCheck should report no errors. Gate two is navigation: every table-of-contents target must open the correct section. Gate three is reflow: text must remain readable after increasing the font size substantially. Gate four is distribution preview: use the preview tool required by the store or library platform you plan to use.

Amazon KDP accepts EPUB manuscripts that meet its publishing guidelines and recommends Kindle Previewer before upload. That store-specific preview complements EPUBCheck; neither replaces an editorial review for missing text, incorrect chapter order, or inaccessible image descriptions.