.epub — Electronic Publication
Document application/epub+zip
What a .epub file is
The open ebook standard — essentially a ZIP of HTML and CSS, so text reflows to fit any screen size.
How to open it
Apple Books, Calibre, Google Play Books, most e-readers except Kindle.
Worth knowing
Kindle uses its own formats. Calibre converts EPUB to them, or you can email the EPUB to your Kindle address.
How to identify a .epub file
A file's extension is only its name — renaming a.png to a.epub changes nothing inside. What software actually reads is the magic number, the first few bytes of the file.
| Signature | 50 4B 03 04 |
| MIME type | application/epub+zip |
| Category | Document |
Also a ZIP, with "mimetype" as the first stored entry.
# what is this file really?
file mystery.epub
# look at the first bytes yourself
xxd mystery.epub | head -2
head -c 16 mystery.epub | xxd
# Windows PowerShell
Get-Content mystery.epub -AsByteStream -TotalCount 16 | Format-HexFrequently asked questions
What is a .epub file?
The open ebook standard — essentially a ZIP of HTML and CSS, so text reflows to fit any screen size.
How do I open a .epub file?
Apple Books, Calibre, Google Play Books, most e-readers except Kindle.
Is .epub safe to open?
Yes. A .epub file is data, not code — opening one cannot execute anything by itself.
Can I change a file's extension to convert it?
No. Renaming changes the label, not the bytes. The one place it appears to work is between formats that genuinely share a container — renaming .docx to .zip works because a DOCX is a ZIP. Everything else needs a real converter.