[3] On 31 October 2006, when Sony introduced its PRS-500 e-reader, Kovid Goyal started developing libprs500, aiming mainly to enable use of the PRS-500 formats on Linux.

[4] With support from the MobileRead forums, Goyal reverse-engineered the proprietary Broad Band eBook (BBeB) file format.

Metadata can be pulled from many different sources, e.g. ISBNdb.com; online booksellers; and providers of free e-books and periodicals in the US and elsewhere, such as the Internet Archive, Munsey's Magazine, and Project Gutenberg; and social networking sites for readers, such as Goodreads and LibraryThing.

E-books can then be exported to all supported reading devices via USB, Calibre's integrated mail server, or wirelessly.

Mailing e-books enables, for example, sending personal documents to the Amazon Kindle family of e-readers and tablet computers.