This article provides a brief introduction to the EPUB format (EPUB 2 and EPUB 3 standards), how EPUB differs from other digital book formats, book design considerations and ebook readers supporting EPUB. The article is intended for publishers and production managers without an IT background. 

1. What is “EPUB”?

EPUB is a format for digital books. It is an XML format that has been defined by the International Digital Publishing Form (IDPF) (, which is the international standards committee for digital publishing.

2. What is XML format, and what does it mean for books?

XML is a kind of programming language that is text-based and semantic (ie meaningful). It enables information to be structured in a standard way so that it can be easily exchanged between systems without knowledge of specific hardware or software. That means the same XML file can be used and displayed on multiple platforms, as long as the file conforms to the rules of the XML document defining the type of information. These rules are called the Document Definition Type (DTD), and a file that conforms to a DTD is said to be valid.

EPUB books are text files that are structured according to the EPUB DTD, as defined by the IDPF, and they end in the filename extension .epub. Valid .epub files can then be used on any platform or device that supports EPUB.

The structure and language for the XML files defined by EPUB are specific to books. For example, sections within a book are denoted by the <chapter> tag. By contrast, scholarly journal DTDs define journal sections by <abstract> and <article> tags (there’s more to it than this, but you get the idea – this is what is meant by a semantic language).

3. What is the difference between EPUB 2 and EPUB 3? 

The most common EPUB standard currently in use is version 2.0.1. This version is supported by most ebook readers on the market at the start of 2012 (see item 8 below).

In October 2011, the IDPF released EPUB 3 to replace the previous version. According to the IDPF, “The expectation is that EPUB 3 will be utilized for a broad range of content, including books, magazines and educational, professional and scientific publications.” ( This is because the changes allow for the inclusion of embedded multimedia files (audio and video), mathML (an XML markup language for mathematical notations), and font embedding, among other things. An overview of all the changes is available at

At the time of writing (January 2012), only Apple’s iBooks app for the iPad supports EPUB 3, and this is as much to do with hardware as software. The prescribed video and audio formats in EPUB 3 are those specified in the HTML5 standard. Among tablets, the iPad uses HTML5 video while others tend to use Flash video, and very few non-tablet ebook readers support any kind of video or audio. Whilst this will undoubtedly change given time for device manufacturers to implement HTML5, since EPUB 2 will be with us for some time to come, the rest of this discussion relates to the EPUB 2 standard.

4. How are EPUB files different from other types of digital book files?

The main difference between EPUBs and other types of digital book files, from a user perspective, is that EPUB books do not define pages, so that the text can easily reflow and resize to suit different types of digital book readers – it’s a kind of “one size fits all” format.

There are some other types of digital book files that also reflow, eg XML files defined according to different DTDs, such as the DAISY format, and PDF files that are set to reflow. However, the two most common (non-XML) digital book formats are PDF which is deliberately set not to reflow so that page integrity is maintained, and web HTML which tends to be defined by the page (though there may be reflow within browser windows).

EPUBs do contain defined sections of course, such as chapters; an EPUB file is actually a collection of files arranged according to the order defined in the navigation file, and each new file (generally, but not always, a new section such as a chapter) opens as a new “page”, whether it looks like a single page or 50 within a particular device.

5. What are the effects of no page definition on book production and layout?

The lack of page definition has several implications for book design:

  • there are no running headers or footers (though these can be set at application level to display the current section);
  • there are no set page numbers that correspond to the screen view: the reader’s place within the text is shown in different ways depending on the application;
  • layout is simplified: there is only ever 1 column of text, and images are not positioned in particular places alongside text, but are “in line” (but see below);
  • footnotes cannot be placed at the bottom of the relevant page, but can be positioned immediately following the relevant paragraph, or they can become numbered endnotes hyperlinked to the number in the text.

If you are used to producing layouts that depend heavily on positioning of text, images and other elements within the page, you may need to rethink this approach when doing EPUB books. In other words, redesign your book’s layout specifically for EPUB. This is much simpler if you are using an XML-first workflow.

Note that fixed layout EPUBs, which support more complex layouts as found in print, are not part of the IDPF standard but are extensions to the standard specific to some ebook apps such as iBooks. (My own preference is for re-designing a book for reading across a variety of apps in standard EPUB, and offering a fixed-layout PDF as well, rather than going to the efforts and expense of reproducing a print layout in EPUB for limited application. That kind of energy could be put into producing an app version of the book instead.)

6. Do I need special software and systems to produce an .epub file?

There is no single answer to this; it depends on what systems and software you are already using, your technical and production expertise, and how fussy you are about the quality of the outcome.

For example, industry-standard typesetting applications either already support .epub file export (eg Adobe InDesign), or will do so soon. Or you can use specialist XML and CSS editing tools if you are comfortable with those.  Whatever your tools, you still need to take account of the design factors listed above, and also that all your text uses styles, including character styles for italics, bold, superscript, etc.

If you outsource your typesetting, your typesetter may be able to produce EPUB files for you, or you can choose to outsource EPUB conversion of your files to another service provider. There is no shortage of EPUB conversion suppliers.

There are also low-cost applications that offer to convert PDFs to EPUBs. The quality of the output varies (and also depends on the quality of the file supplied), and you may have to do a lot of post-conversion work on the file. See Ebook conversion: the basics for more on some of the pitfalls of this approach.

Large publishers may choose to develop their own in-house production systems, especially if they already have XML-based systems and in-house technical expertise, while small to medium publishers might prefer to work with technology partners on in-house solutions.

Whether you produce your own EPUB files or have someone else do it for you, you need to make sure the process includes validation (see item 2 above) and user testing.

7. Are all books suitable for EPUB?

At present, simple text-based books such as novels and standard non-fiction books are easiest to produce as EPUBs because they are less limited by the design considerations noted above (item 5). They are also easiest to read on EPUB reading devices as they lend themselves to immersive reading.

Graphic-rich textbooks and illustrated children’s books are probably the most difficult to produce as EPUBs right now, and publishers of such books are producing digital versions in other ways that incorporate multimedia (notably multimedia “apps”). As EPUB 3 gains wider application support, we will probably start to see more complex books widely available as EPUBs.

Publishers of scientific, legal and reference material are well advanced in producing xml-based files published on their own platforms and in web-based browser platforms, with greater functionality than currently offered by EPUB readers. With EPUB 3, such publishers are now well-placed to convert their XML publications to EPUB (see item 3 above and item 8 below).

8. Where can I see examples of EPUB books?

EPUB books need EPUB compatible software (aka applications or “apps”). There are a number of such apps available, which are either pre-installed on a hardware device (desktop, laptop, tablet or ebook reader) or available for download onto a hardware device. This is not as complicated as it sounds – it is in fact no different from needing Microsoft Word to read .doc files, Adobe Reader to read .pdf files, or a web browser such as Firefox or Safari to read .html files (see previous post: Ebook formats: the basics). In fact some EPUB reader platforms, such as Google Books, and Tizra, are also browser-based.

The following list of EPUB applications, listed alphabetically, makes no distinction between downloadable or pre-installed software, nor commercial availability. It is also not exhaustive. Most have free books to view, as well as for purchase.

  • Adobe Digital Editions
  • Apple iBooks
  • Barnes & Noble’s Nook
  • Kobo
  • Sony eReader
  • Stanza

Free EPUBs are also available from Project Gutenberg, but you will need one of the above EPUB readers to use them. There are other digital book devices around that support different XML-based formats, most notably Amazon’s Kindle and DAISY. Conversion from the EPUB format to another XML-based format is relatively straightforward.

9. What can I do with my EPUB book files once I have produced them?

Assuming you wish to sell your books, you will need an agreement in place with one or more EPUB book vendors, either directly or via a distributor. Alternatively, you may have your own sales platform in place. Commercial platforms allow buyers to download the book files to their ereader or access the file online via a “cloud” service. Usually some kind of sharing and copying restrictions (known as DRM – “digital rights management”) will be in place.

If you wish to give your EPUB books away, then you only need to place them online for readers to download, as Project Gutenberg does (with advice on formats and readers).

Where can I find out more?

Information on the EPUB standard is found on the IDPF website (

Help with EPUB production or conversion is readily available online. You may want to join one of the many ebook and EPUB groups on Linked In and find an expert and/or ask the group for advice. If you are a publisher, author or designer, your relevant industry association should be able to help.

For assistance with downloading, buying or using EPUB books, or using EPUB reader apps, see the specific vendor websites.

Note: This article is a revision of my 2010 article EPUB: getting started.

© 2012 Linda Kythe Nix. All rights reserved.