EPUB 3.0

"The EPUB® specification is a distribution and interchange format standard for digital publications and documents. EPUB defines a means of representing, packaging and encoding structured and semantically enhanced Web content — including HTML5, CSS, SVG, images, and other resources — for distribution in a single-file format."

EPUB 3.0 | International Digital Publishing Forum

EPUB 3 was developed pursuant to a charter approved by the IDPF Membership in May, 2010. EPUB 3.0 was approved by the IDPF membership as a final Recommended Specification effective October 11, 2011, and superseded the previous release of EPUB (2.0.1). 

 EPUB 3.0.1, which is now the current version of the EPUB standard. 

The best starting point for learning about EPUB 3.0, including the roadmap to the specification documents, is the EPUB 3 Overview .