.EPUB File Extension

An EPUB file is a digital ebook saved in the EPUB format, an open XML-based format for digital books and publications. It provides a standard digital publication format for publishers and consumers. EPUB files can be viewed with supporting software programs and hardware devices, such as the Sony Reader and Barnes & Noble Nook.

The EPUB format is based on three open standards, which are all maintained by the International Digital Publishing Forum (IDPF).

1. The Open Publication Structure (OPS), which defines the content markup
2. The Open Packaging Format (OPF), which describes the ebook structure
3. The Open Container Format (OCF), which packages all the ebook files together in a compressed format

NOTE: Many commercial ebooks include digital rights management (DRM) protection. These files can only be opened on devices that have been authorized to view the ebook.