EPUB
EPUB is the most widely adopted ebook file format. Initially developed by the International Digital Publishing Forum (which is now part of the World Wide Web Consortium), it superseded the old Open ebook format (OEB) in 2007. Because EPUB is free to use, open standard, and vendor-independent, it has grown to become the most common ebook format. In many ways, it’s the ebook equivalent of the trusty MP3. Almost all mainstream e-readers and computer operating systems support the format.
MOBI
Like EPUB, the MOBI format also grew out of the old OEB format. French company Mobipocket went on to form the basis of its Mobipocket Reader software. There are a few key differences between EPUB and MOBI. Most pertinently, it is not open standard and, therefore, is not publicly available. It also cannot support sound or video. Once again, it’s supported by all the major e-readers with one exception: the Barnes and Noble Nook.