The key IDPF standard is EPUB®, the current version is EPUB 3.1.
EPUB is the distribution and interchange format standard for digital publications and documents based on Web Standards. EPUB defines a means of representing, packaging and encoding structured and semantically enhanced Web content — including XHTML, CSS, SVG, images, and other resources — for distribution in a single-file format. EPUB allows publishers to produce and send a single digital publication file through distribution and offers consumers interoperability between software/hardware for unencrypted reflowable digital books and other publications.
The community and news site for the EPUB ecosystem is http://epubzone.org.
EPUB 2 was initially standardized in 2007 as a successor format to the Open eBook Publication Structure or "OEB", which was originally developed in 1999. A maintenance release, EPUB 2.0.1, approved in 2010, was the final release in the EPUB 2 branch.
In October, 2011, EPUB 3 superseded EPUB 2 when EPUB 3.0 was approved as a final Recommended Specification. A maintenance release, EPUB 3.0.1, was approved as a Final Recommended specification in June, 2014.
In January 2017, EPUB 3.1, the first major update to EPUB 3, was approved as a Recommended Specification. It is the current version of the standard.