EPUB (short for electronic publication) is a free and open e-book standard by the International Digital Publishing Forum (IDPF). Files have the extension .epub.
EPUB is designed for reflowable content, meaning that an EPUB reader can optimize text for a particular display device. EPUB also supports fixed-layout content. The format is intended as a single format that publishers and conversion houses can use in-house, as well as for distribution and sale. It supersedes the Open eBook standard.
On April 6, 2010, it was announced that a working group would form to revise the EPUB specification. In the working group’s charter draft, 14 main problems with EPUB are identified, which the group will address. The group was chartered through May 2011, and was scheduled to submit a final draft on May 15, 2011. An initial Editors Draft for EPUB3 was published on November 12, 2010, and the first public draft was published on February 15, 2011. On May 23, 2011, the IDPF released its proposed specification for final review. On October 10, 2011, the IDPF announced that its membership had approved EPUB 3 as a final Recommended Specification.
The EPUB 3.0 Recommended Specification was approved on 11 October 2011. EPUB 3.0 supersedes the previous release 2.0.1 of EPUB. Detailed descriptions of the differences between 3.0 and 2.0.1 can be found on the IDPF website.
EPUB 3 consists of a set of four specifications:
EPUB Publications 3.0, which defines publication-level semantics and overarching conformance requirements for EPUB Publications
EPUB Content Documents 3.0, which defines profiles of XHTML, SVG and CSS for use in the context of EPUB Publications
EPUB Open Container Format (OCF) 3.0, which defines a file format and processing model for encapsulating a set of related resources into a single-file (ZIP) EPUB Container.
EPUB Media Overlays 3.0, which defines a format and a processing model for synchronization of text and audio