Now that I’ve been on all three sides of the digital book business, as reader, author, and publisher, I realize how confusing some of the technology can be.
So here’s the first in a series of posts on digital publishing in general and in specific.
Today’s topic: file formats.
The acknowledged open standard for ebooks is EPUB, which superseded the Open eBook standard in September 2007. EPUB is developed and managed by the International Digital Publishing Forum (IDPF). That group has a membership of more than 300, including a who’s who of traditional publishing, open source advocates, publishing tool makers, font companies, and more. Adobe, Apple, and Microsoft are all members. Amazon is not.
Apple has used the EPUB format exclusively since its introduction of iBooks in April 2010. At the time, Apple called EPUB “the most popular open book format in the world,” and today it refers to EPUB as “the industry-leading … digital book file type.”
With the release of iBooks Author in January 2012, Apple has introduced a new, proprietary ebook format that is based on EPUB but is incompatible with software and hardware designed to use EPUB. The iBooks reader still supports DRM-free EPUB files, regardless of their source.
Every Android-based device I’ve seen supports EPUB directly, including the Barnes and Noble Nook Color and Nook Tablet.
Amazon’s popular Kindle devices do not support EPUB format directly. (This limitation applies to the Kindle Fire as well, despite the fact that its operating system is an Amazon-customized version of Android.) The default format on the Kindle is Amazon’s proprietary AZW. Kindles do, however, support the MOBI format (.mobi), which was originally developed by Mobipocket, which was purchased by Amazon in 2005.
Some e-book distributors (including Fair Trade DX and O’Reilly, where my books are sold) include MOBI files in their retail offerings. You can also use software to convert EPUB to MOBI format. I use and recommend the free, open source Calibre ebook management program for this and many other tasks.
The preceding formats are all designed for use with reflowable content, meaning that fonts and graphics shift to adapt to the display. So you can read the same ebook on a smartphone, a tablet, a dedicated reader, or a PC/Mac.
Reflowable content works great with fiction or books that include inline illustrations. It’s not so good for projects where the designer wants to control the precise arrangement of each page, including fonts. For that purpose, the best choice is still a PDF file.
There are many more digital book formats (see this Wikipedia article for an exhaustive list), but those are the ones that matter.
Digital rights management (DRM), aka copy protection, is an optional feature in the AZW and EPUB formats (and, presumably, in the new iBooks format). None of the digital editions of my books include DRM, but that’s a topic for another day.
Plug: My latest book, Windows 8 Head Start, is available in a downloadable package that includes three DRM-free digital formats for 30% off its $9.95 list price, with a free update to the next edition. Details are here.
Ed Bott (@ wordpress.com) 
First, one typo – you said “With the release of iBooks Author in January 2011,…”. I think you mean 2012.
Then, what looks like a contradiction.
“Every Android-based device I’ve seen supports EPUB directly, including the Kindle Fire…”
but then
“Amazon’s popular Kindle devices do not support EPUB format directly”.
A Kindle Fire is a popular Kindle device but, from what you say, it both does and does not support EPUB directly. Which is it?
Jon, thanks for that note. I corrected the 2012 reference. (If I still wrote checks I would have made that mistake many times already.)
Also clarified that the Kindle Fire, which is Android-powered, is different from other Kindle devices but still lacks support for EPUB. Thanks for inspiring me to triple-check that.
Good primer, Ed. I’m glad that you described the weakness of the eBook formats for static formatting (and how PDF is still the best format for that). I especially liked the links to the Wikipedia article and Calibre (which I use and love to convert between formats, and even to read on my laptop).
I have a question though. I haven’t looked at iBook Author (and I don’t own any device to use it anyway), but I’d understood that iBook Author addresses the static formatting limitations in traditional ePub documents. Have you tried this yourself?
TaMan,
I am looking at iBooks Author and will have a detailed post on its primary format at ZDNet tomorrow. Short version: it’s a bastardized version of EPUB with just enough incompatibilities (and a restrictive license agreement) to make it suitable only for use with the iBooks 2 reader on iPads and other iOS devices. It will not work with any other reader. That’s not a value judgment, it’s a technical reality.
As I explained to another commenter, I went to great pains to make this post a neutral explainer about file formats. I want this information to be of value to people who are confused by a new technology. I do not want the comments section to turn into a flamefest over Apple, Amazon, or any other company.
Thanks to all my readers for their understanding.
Ed, if I understand the current standards for ebooks correctly, it seems they are rather restrictive still. Suppose that I wanted to make a science book with animations, sound, intelligent tutors, etc. Why not just use html as the standard? I guess I’m just asking you’re advice before I start my own book. Maybe you know someone who has made a non-traditional book in an e format? Sorry if I made some errors in this text…. getting used to my.new kindle 🙂 just thinking about creating my first book…