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In October, 2011, EPUB 3 superseded EPUB 2 when EPUB 3.0 was approved as a final Recommended Specification.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 and became the current version of EPUB in June, 2014.