Whenever possible, we provide an ebook version in the form of an EPUB. An EPUB is the most common file type for ebooks. EPUB files can be opened with almost any ebook reader, with the very important exception of Kindle (although some apps have been developed for Kindle Fires that will open EPUB ebooks). This ebook format is highly flexible and can include interactive features—though not all devices and readers can support them. The most important feature about the EPUB type of ebook is that it is reflowable. This means it has many of the qualities people love about ebooks: the reader can control the font face, size, and color. Some ebook readers even let you add highlighting and notes.
EPUBs are specifically designed to be flexible and read on smartphones, tablets, and dedicated e-reader devices. But they can also be read on computers using iBooks on Mac OS X and Calibre for Mac, Windows, and Linux. There are also web browser-based EPUB readers, such as Google Play Books (you can upload your own EPUB files), and the browser add-on Readium.
Lastly, an EPUB is an open standard, making it relatively easily used, opened, and adapted. In essence, the ebook is a self-contained webpage: a collection of .xhtml files. The book can be “unzipped,” and the source files accessed (the method on Windows and Mac are different for this process, but both are fairly straightforward).
Calibre and Sigil are two free applications that allow users to open and edit EPUB files without unzipping or accessing the .xhtml files.
There are also many online services that allow users to create EPUB files from Word Documents, blogs, and more, such as PressBooks, LeanPub, FastPencil, and Papyrus.