The ePUB standard is an open format for electronic books from the International Digital Publishing Forum (IDPF). Stanza for iPhone and iPod Touch supports ePUB files natively, and Lexcycle is one of the member companies of the IDPF. ePUB is currently the only format of books that Stanza iPhone can read. Stanza Desktop also supports ePUB among about a dozen other formats. Individuals often use Stanza Desktop or other tools to convert other formats to ePUB and then use Stanza Desktop to share them with Stanza iPhone.

We often get questions about whether or not a file is a valid ePUB file. Adobe has written a tool to help with this called EpubCheck. Unless you are technically inclined, it is a bit of work to use EpubCheck directly (for example, one option is to deploy it with Tomcat). That has now changed. bookworm recently made EpubCheck available via the web.