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. An EPUB file uses XHTML 1.1 (or DTBook) to construct the content of a book as of version 2.0.1. This is different from previous versions (OEBPS 1.2 and earlier), which used a subset of XHTML. There are, however, a few restrictions on certain elements. The mimetype for XHTML documents in EPUB is application/xhtml+xml.
The digital book format originally used by Sony Corporation. It is a proprietary format, but some reader software for general-purpose computers, particularly under Linux (for example, calibre's internal viewer), have the capability to read it. The LRX file extension represents a DRM encrypted eBook. More recently, Sony has converted its books from BBeB to EPUB and is now issuing new titles in EPUB.