Glossary · Printing & files
What is an EPUB file?
Definition
EPUB: EPUB is the standard open file format for eBooks. It is accepted by Apple Books, Kobo, Google Play, Barnes & Noble and Amazon KDP.
EPUB (short for electronic publication) is the open, industry-standard format for eBooks, maintained today under the W3C. An EPUB file is essentially a zipped package of web-style content — HTML text, CSS styling, images and a metadata file — which reading apps can resize and restyle on any screen. EPUB 3 is the current version.
Nearly every eBook store accepts EPUB uploads, including Apple Books, Kobo, Google Play Books and Barnes & Noble Press, and aggregators such as Draft2Digital. Amazon KDP also accepts EPUB and converts it into its own Kindle format; Amazon has moved away from accepting the older MOBI format for new reflowable eBooks, so check KDP's current list of supported formats.
A good EPUB has a working, clickable table of contents, correct chapter breaks, embedded metadata (title, author, language, identifier), a cover image, and clean styling that does not fight the reader's own font and size settings. Stores and distributors often run files through EPUBCheck, the standard validation tool, and may reject files that fail.
Most self-published novels and nonfiction books are EPUB in reflowable layout. Picture books, comics and heavily designed cookbooks may use fixed layout instead.