FILE FORMAT GUIDE
EPUB File (.EPUB): What It Is & How to Open It
An EPUB file is a ZIP-based Open Container Format package for an electronic publication. It combines package metadata, reading order and publication resources.
Check for the reviewed ZIP container signature. This confirms the container, not the inner EPUB Publication structure.
Check supported file headersQuick facts
- Extension
- .epub
- Format
- EPUB Publication
- Category
- document
- MIME type
- application/epub+zip
- Standard / developer
- W3C
- Open with
- Calibre E-book Viewer
What is EPUB?
A conforming EPUB puts an uncompressed mimetype entry first and stores application/epub+zip in it. The package can contain active or externally referenced content, so listing ZIP entries is not equivalent to safe rendering.
How to open EPUB
Calibre E-book ViewerWindows / macOS / Linux
Add the EPUB to Calibre or open it directly in the E-book Viewer. Copy-protected books may require the vendor application tied to the purchase.
Common uses and compatibility
- Deliver a reflowable or fixed-layout electronic publication and its resources
Things to check
- Container validity does not guarantee content accessibility, correct reading order or safe handling by every reading system.
Advanced inspection
These developer and command-line workflows inspect structure or metadata. They are not the default way most people open the file.
EPUBCheckCommand-line tool or library
Run epubcheck book.epub to check the publication against supported EPUB rules. Treat a clean report as conformance evidence, not as a malware scan or rights clearance.
Technical details
- Signature
- 50 4B 03 04 at offset 0; mimetype at offset 30; application/epub+zip at offset 38
- Encoding
- Not applicable
- Container
- EPUB Open Container Format ZIP
- Compression
- Stored or Deflate ZIP entries
Related formats
- Portable Document Format
PDF is commonly fixed-layout, while EPUB packages publication resources for reading-system workflows that may reflow.
- XML Paper Specification Document
XPS is a fixed-layout document package, while EPUB is a publication package designed for reading systems.
Sources & review
Sources reviewed 2026-09-19.