EPUB is an e-book file format that uses the ".epub" file extension. The term is short for electronic publication and is sometimes styled ePub. EPUB is supported by many e-readers, and compatible software is available for most smartphones, tablets, and computers. EPUB is a technical standard published by the International Digital Publishing Forum (IDPF). It became an official standard of the IDPF in September 2007, superseding the older Open eBook standard.[2]

The Book Industry Study Group endorses EPUB 3 as the format of choice for packaging content and has stated that the global book publishing industry should rally around a single standard.[3] The EPUB format is implemented as an archive file consisting of HTML files carrying the content, along with images and other supporting files. EPUB is the most widely supported vendor-independent XML-based (as opposed to PDF) e-book format; that is, it is supported by the largest number of hardware readers.

Electronic Publication (EPUB)
EPUB logo
Filename extension.epub
Internet media typeapplication/epub+zip
Magic numberPK\x03\x04 (Zip)
Developed byInternational Digital Publishing Forum (IDPF)
Initial releaseSeptember 2007
Latest release
(January 5, 2017[1])
Type of formate-book file format
Contained byOEBPS Container Format (OCF; Zip)
Extended fromOpen eBook, XHTML, CSS, DTBook
StandardISO/IEC TS 30135
Open format?Yes


A successor to the Open eBook Publication Structure, EPUB 2.0 was approved in October 2007,[4] with a maintenance update (2.0.1) approved in September 2010.[5]

The EPUB 3.0 specification became effective in October 2011, superseded by a minor maintenance update (3.0.1) in June 2014.[6] New major features include support for precise layout or specialized formatting (Fixed Layout Documents), such as for comic books,[7] and MathML support. The current version of EPUB is 3.1, effective January 5, 2017.[8] The (text of) format specification underwent reorganization[9] and clean-up; format supports remotely-hosted resources and new font formats (WOFF 2.0 and SFNT)[10] and uses more pure HTML and CSS.[11]

In May 2016 IDPF Members approved World Wide Web Consortium (W3C) merger,[12] "to fully align the publishing industry and core Web technology".[13]

Version 2.0.1

EPUB 2.0 was approved in October 2007, with a maintenance update (2.0.1) intended to clarify and correct errata in the specifications being approved in September 2010.[5] EPUB version 2.0.1 consists of three specifications:

  • Open Publication Structure (OPS) 2.0.1, contains the formatting of its content.[14]
  • Open Packaging Format (OPF) 2.0.1, describes the structure of the .epub file in XML.[15]
  • Open Container Format (OCF) 2.0.1, collects all files as a ZIP archive.[16]

EPUB internally uses XHTML or DTBook (an XML standard provided by the DAISY Consortium) to represent the text and structure of the content document, and a subset of CSS to provide layout and formatting. XML is used to create the document manifest, table of contents, and EPUB metadata. Finally, the files are bundled in a zip file as a packaging format.

Open Publication Structure 2.0.1

An EPUB file uses XHTML 1.1 (or DTBook) to construct the content of a book as of version 2.0.1. This is different from previous versions (OEBPS 1.2 and earlier), which used a subset of XHTML. There are, however, a few restrictions on certain elements. The mimetype for XHTML documents in EPUB is application/xhtml+xml.[14][a]

Styling and layout are performed using a subset of CSS 2.0, referred to as OPS Style Sheets. This specialized syntax requires that reading systems support for only a portion of CSS properties and adds a few custom properties. Custom properties include oeb-page-head, oeb-page-foot, and oeb-column-number. Font-embedding can be accomplished using the @font-face property, as well as including the font file in the OPF's manifest (see below). The mimetype for CSS documents in EPUB is text/css.[14][b]

EPUB also requires that PNG, JPEG, GIF, and SVG images be supported using the mimetypes image/png, image/jpeg, image/gif, image/svg+xml. Other media types are allowed, but creators must include alternative renditions using supported types.[14] For a table of all required mimetypes, see Section 1.3.7 of the specification.

Unicode is required, and content producers must use either UTF-8 or UTF-16 encoding.[14] This is to support international and multilingual books. However, reading systems are not required to provide the fonts necessary to display every unicode character, though they are required to display at least a placeholder for characters that cannot be displayed fully.[14]

An example skeleton of an XHTML file for EPUB looks like this:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
    <meta http-equiv="Content-Type" content="application/xhtml+xml; charset=utf-8" />
    <title>Pride and Prejudice</title>
    <link rel="stylesheet" href="css/main.css" type="text/css" />

Open Packaging Format 2.0.1

The OPF specification's purpose is to "...[define] the mechanism by which the various components of an OPS publication are tied together and provides additional structure and semantics to the electronic publication."[15] This is accomplished by two XML files with the extensions .opf and .ncx.

.opf file

The OPF file, traditionally named content.opf, houses the EPUB book's metadata, file manifest, and linear reading order. This file has a root element package and four child elements: metadata, manifest, spine, and guide. Furthermore, the package node must have the unique-identifier attribute. The .opf file's mimetype is application/oebps-package+xml.[15]

The metadata element contains all the metadata information for a particular EPUB file. Three metadata tags are required (though many more are available): title, language, and identifier. title contains the title of the book, language contains the language of the book's contents in RFC 3066 format or its successors, such as the newer RFC 4646 and identifier contains a unique identifier for the book, such as its ISBN or a URL. The identifier's id attribute should equal the unique-identifier attribute from the package element.[15][c]

The manifest element lists all the files contained in the package. Each file is represented by an item element, and has the attributes id, href, media-type. All XHTML (content documents), stylesheets, images or other media, embedded fonts, and the NCX file should be listed here. Only the .opf file itself, the container.xml, and the mimetype files should not be included.[15] Note that in the example below, an arbitrary media-type is given to the included font file, even though no mimetype exists for fonts.

The spine element lists all the XHTML content documents in their linear reading order. Also, any content document that can be reached through linking or the table of contents must be listed as well. The toc attribute of spine must contain the id of the NCX file listed in the manifest. Each itemref element's idref is set to the id of its respective content document.[15]

The guide element is an optional element for the purpose of identifying fundamental structural components of the book. Each reference element has the attributes type, title, href. Files referenced in href must be listed in the manifest, and are allowed to have an element identifier (e.g. #figures in the example).[15][d]

An example OPF file:

<?xml version="1.0"?>
<package version="2.0" xmlns="http://www.idpf.org/2007/opf" unique-identifier="BookId">

  <metadata xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:opf="http://www.idpf.org/2007/opf">
    <dc:title>Pride and Prejudice</dc:title>
    <dc:identifier id="BookId" opf:scheme="ISBN">123456789X</dc:identifier>
    <dc:creator opf:file-as="Austen, Jane" opf:role="aut">Jane Austen</dc:creator>

    <item id="chapter1" href="chapter1.xhtml" media-type="application/xhtml+xml"/>
    <item id="stylesheet" href="style.css" media-type="text/css"/>
    <item id="ch1-pic" href="ch1-pic.png" media-type="image/png"/>
    <item id="myfont" href="css/myfont.otf" media-type="application/x-font-opentype"/>
    <item id="ncx" href="toc.ncx" media-type="application/x-dtbncx+xml"/>

  <spine toc="ncx">
    <itemref idref="chapter1" />

    <reference type="loi" title="List Of Illustrations" href="appendix.html#figures" />


.ncx file

The NCX file (Navigation Control file for XML), traditionally named toc.ncx, contains the hierarchical table of contents for the EPUB file. The specification for NCX was developed for Digital Talking Book (DTB), is maintained by the DAISY Consortium, and is not a part of the EPUB specification. The NCX file has a mimetype of application/x-dtbncx+xml.

Of note here is that the values for the docTitle, docAuthor, and meta name="dtb:uid" elements should match their analogs in the OPF file. Also, the meta name="dtb:depth" element is set equal to the depth of the navMap element. navPoint elements can be nested to create a hierarchical table of contents. navLabel's content is the text that appears in the table of contents generated by reading systems that use the .ncx. navPoint's content element points to a content document listed in the manifest and can also include an element identifier (e.g. #section1).[15][17]

A description of certain exceptions to the NCX specification as used in EPUB is in Section 2.4.1 of the specification. The complete specification for NCX can be found in Section 8 of the Specifications for the Digital Talking Book.[17]

An example .ncx file:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE ncx PUBLIC "-//NISO//DTD ncx 2005-1//EN"

<ncx version="2005-1" xml:lang="en" xmlns="http://www.daisy.org/z3986/2005/ncx/">

<!-- The following four metadata items are required for all NCX documents,
including those that conform to the relaxed constraints of OPS 2.0 -->

    <meta name="dtb:uid" content="123456789X"/> <!-- same as in .opf -->
    <meta name="dtb:depth" content="1"/> <!-- 1 or higher -->
    <meta name="dtb:totalPageCount" content="0"/> <!-- must be 0 -->
    <meta name="dtb:maxPageNumber" content="0"/> <!-- must be 0 -->

    <text>Pride and Prejudice</text>

    <text>Austen, Jane</text>

    <navPoint class="chapter" id="chapter1" playOrder="1">
      <navLabel><text>Chapter 1</text></navLabel>
      <content src="chapter1.xhtml"/>


Open Container Format 2.0.1

An EPUB file is a group of files that conform to the OPS/OPF standards and are wrapped in a ZIP file.[18] The OCF specifies how to organize these files in the ZIP, and defines two additional files that must be included.

The mimetype file must be a text document in ASCII that contains the string application/epub+zip. It must also be uncompressed, unencrypted, and the first file in the ZIP archive. This file provides a more reliable way for applications to identify the mimetype of the file than just the .epub extension.[16]

Also, there must be a folder named META-INF, which contains the required file container.xml. This XML file points to the file defining the contents of the book. This is the OPF file, though additional alternative rootfile elements are allowed.[16]

Apart from mimetype and META-INF/container.xml, the other files (OPF, NCX, XHTML, CSS and images files) are traditionally put in a directory named OEBPS.

An example file structure:

--ZIP Container--

An example container.xml, given the above file structure:

<?xml version="1.0" encoding="UTF-8" ?>
<container version="1.0" xmlns="urn:oasis:names:tc:opendocument:xmlns:container">
    <rootfile full-path="OEBPS/content.opf" media-type="application/oebps-package+xml"/>

Version 3.0.1

The EPUB 3.0 Recommended Specification was approved on 11 October 2011. On June 26, 2014 EPUB 3.0.1 was approved as a minor maintenance update to EPUB 3.0. EPUB 3.0 supersedes the previous release 2.0.1.[e]

EPUB 3 consists of a set of four specifications:[19]

  • EPUB Publications 3.0, which defines publication-level semantics and overarching conformance requirements for EPUB Publications
  • EPUB Content Documents 3.0, which defines profiles of XHTML, SVG and CSS for use in the context of EPUB Publications
  • EPUB Open Container Format (OCF) 3.0, which defines a file format and processing model for encapsulating a set of related resources into a single-file (ZIP) EPUB Container.
  • EPUB Media Overlays 3.0, which defines a format and a processing model for synchronization of text and audio

The EPUB 3.0 format was intended to address the following criticisms:

  • While good for text-centric books, EPUB was rather unsuitable for publications that require precise layout or specialized formatting, such as comic books.[7]
  • A major issue hindering the use of EPUB for most technical publications was the lack of support for equations formatted as MathML. They were included as bitmap or SVG images, precluding proper handling by screen readers and interaction with computer algebra systems. Support for MathML is included in the EPUB 3.0 specification.
  • Other criticisms of EPUB were the specification's lack of detail on linking within or between EPUB books, and its lack of a specification for annotation. Such linking is hindered by the use of a ZIP file as the container for EPUB. Furthermore, it was unclear if it would be better to link by using EPUB's internal structural markup (the OPF specification mentioned above) or directly to files through the ZIP's file structure.[20] The lack of a standardized way to annotate EPUB books led to difficulty in sharing and transferring annotations and therefore limited the use scenarios of EPUB, particularly in educational settings, because it cannot provide a level of interactivity comparable to the web.[21]

On June 26, 2014, the IDPF published EPUB 3.0.1 as a final Recommended Specification.[22]

In November 2014, EPUB 3.0 was published by the International Standards Organization as ISO/IEC TS 30135 (parts 1-7).[23]


The format and many readers support the following:

  • Reflowable document: optimize text for a particular display
  • Fixed-layout content:[24] pre-paginated content can be useful for certain kinds of highly designed content, such as illustrated books intended only for larger screens, such as tablets.[25]
  • Like an HTML web site, the format supports inline raster and vector images, metadata, and CSS styling.
  • Page bookmarking
  • Passage highlighting and notes
  • A library that stores books and can be searched
  • Re-sizable fonts, and changeable text and background colors
  • Support for a subset of MathML[26]
  • Digital rights management—can contain digital rights management (DRM) as an optional layer[27]

Digital rights management

An EPUB file can optionally contain DRM as an additional layer, but it is not required by the specifications.[27] In addition, the specification does not name any particular DRM system to use, so publishers can choose a DRM scheme to their liking. However, future versions of EPUB (specifically OCF) may specify a format for DRM.[16]

The EPUB specification does not enforce or suggest a particular DRM scheme. This could affect the level of support for various DRM systems on devices and the portability of purchased e-books. Consequently, such DRM incompatibility may segment the EPUB format along the lines of DRM systems, undermining the advantages of a single standard format and confusing the consumer.[28][29][30][31][32][33]

DRMed EPUB files must contain a file called rights.xml within the META-INF directory at the root level of the ZIP container.[16]


EPUB is widely used on software readers such as Google Play Books on Android and Apple Books on iOS and macOS, but not by Amazon Kindle e-readers. iBooks also supports the proprietary iBook format, which is based on the EPUB format but depends upon code from the iBooks app to function.[34]

Data interchange
EPUB is a popular format for ebook creation because it can be an open format and is based on HTML, as opposed to Amazon's proprietary format for Kindle readers. Popular EPUB producers of public domain and open licensed content, include Project Gutenberg, PubMed Central, SciELO and others.


An EPUB file is an archive that contains, in effect, a website. It includes HTML files, images, CSS style sheets, and other assets. It also contains metadata. EPUB 3 is the latest version. By using HTML5, publications can contain video, audio, and interactivity, just like websites in web browsers.[25]


An ePub publication is delivered as a single file. This file is an unencrypted zipped archive containing a set of interrelated resources.[35]

An OCF (Open Container Format) Abstract Container defines a file system model for the contents of the container. The file system model uses a single common root directory for all contents in the container. All (non-remote) resources for publications are in the directory tree headed by the container's root directory, though EPUB mandates no specific file system structure for this. The file system model includes a mandatory directory named META-INF that is a direct child of the container's root directory. META-INF stores container.xml.

The first file in the archive must be the mimetype file. It must be unencrypted and uncompressed so that non-ZIP utilities can read the mimetype. The mimetype file must be an ASCII file that contains the string "application/epub+zip". This file provides a more reliable way for applications to identify the mimetype of the file than just the .epub extension.[35]

An example file structure:

--ZIP Container--

There must be a META-INF directory containing container.xml. This file points to the file defining the contents of the book, the OPF file, though additional alternative rootfile elements are allowed.[35] Apart from mimetype and META-INF/container.xml, the other files (OPF, NCX, XHTML, CSS and images files) are traditionally put in a directory named OEBPS. An example container.xml:

<?xml version="1.0" encoding="UTF-8" ?>
<container version="1.0" xmlns="urn:oasis:names:tc:opendocument:xmlns:container">
    <rootfile full-path="OEBPS/content.opf" media-type="application/oebps-package+xml"/>


The ePUB container must contain:[36]

  • At least one content document.
  • One navigation document.
  • One package document listing all publication resources. This file should use the file extension .opf. It contains metadata, a manifest, fallback chains, bindings, and a spine. This is an ordered sequence of ID references defining the default reading order.

The ePUB container may contain:


Content documents include:[37] HTML 5 content, navigation documents, SVG documents, scripted content documents, and fixed layout documents. Contents also include CSS and PLS documents. Navigation documents supersedes the NCX grammar used in EPUB 2.

Media overlays

Books with synchronized audio narration are created in EPUB 3 by using media overlay documents to describe the timing for the pre-recorded audio narration and how it relates to the EPUB Content Document markup. The file format for Media Overlays is defined as a subset of SMIL.[38]


Many editors exist including calibre and Sigil, both of which are open source. Another open source tool, called epubcheck, can be used for validating and detecting errors in the structural markup (OCF, OPF, OPS), image, and XHTML files.[39]

Readers exist for all major hardware platforms with the exception of Amazon Kindle, such as Adobe Digital Editions and calibre on desktop platforms, Google Play Books and Aldiko on Android and iOS, and Apple iBooks on macOS and iOS.

Reading software

The following software can read and display EPUB files:

Reading Systems and Software[18]
Software License Platform DRM formats supported Notes
Adobe Digital Editions Proprietary Microsoft Windows, Apple Mac OS X Adobe Content Server Requires online activation for ePub files with DRM.
Aldiko Proprietary Android Adobe Content Server Supports ePub for Android devices.
AZARDI Freeware Windows, OS X, Linux, Android, Apple iOS proprietary ackage obfuscation Supports ePub 3, ePub 2. Fixed Layout, SMIL, DRM, MathML, Online and Mobile versions are available when used with AZARDI:Content Fulfilment Server.
Bluefire Reader Proprietary Apple iOS, Android Adobe Content Server Supports ePub for Android and iOS devices.
calibre GPL Windows, OS X, Linux None Primarily for library management, conversion, and transferring to devices, it includes a reader. "About". Calibre.
Microsoft Edge Proprietary Windows 10 Added as part of Windows 10 version 10.0.14971 (Creators' Update, 2017)
EPUBReader Custom Mozilla Firefox None Firefox add-on, so runs on any OS that Firefox runs on. EPUBReader home page
FBReader Proprietary Windows, Linux, Android, PDAs, OS X None
Google Play Books Proprietary Web application, Android, Apple iOS Lektz DRM Supports downloading purchased books as ePub and/or PDF.
iBooks Proprietary OS X, iOS FairPlay[40] Supports EPUB 2 and EPUB 3. Books not readable directly on computers other than Macs.
Kitabu GPL OS X None Supports ePub3, ePub2, Fixed layout.
Kobo Proprietary Windows, OS X, Android, Apple iOS, Kobo eReader Software, Adobe Content Server Supports EPUB 2 and EPUB 3.
Lektz Readers Proprietary Web application, Google Android, OS X, iOS, Windows Lektz eBook Readers for PDF, ePUB/2 and ePUB3 providing uniform experience across different platforms - iOS, Android, Windows PC, Mac Desktop and Web.
Lucifox GPL Windows, OS X, Linux None Ebook reader add-on with annotations for Firefox. Supports open standard ebooks in EPUB 3- and EPUB 2 format and retrieval of books from OPDS book catalogues.
Okular GPL Windows, OS X, Linux unknown
Readium BSD All web browsers and all platforms Multiple-DRM implementations Exists as a cross-browser solution for embedding in users’ websites (Readium CloudReader), a Chrome extension and a cross-platform SDK.
Snapplify Proprietary All Web browsers, Apple iOS, Android Adobe Content Server Snapplify SnappSafe DRM Supports downloading purchased books as ePub and/or PDF. Supports PDF, ePUB2 and ePUB3 standard of ebooks.
STDU Viewer Freeware Windows Supports many documents format including ePub.
Sumatra PDF GPL Windows Adobe Content Server Supports ePub for devices.

See also the Wikipedia category for articles about EPUB readers.

Editing software

Creation Software
Software Platform License Notes
ABBYY FineReader Microsoft Windows Proprietary Version 11 exports to EPUB format.
Abiword FreeBSD, Linux, Windows GPL Support EPUB 2.0 format export since 2.9.1 release[41]
Adobe InDesign Windows, OS X Proprietary Exports to EPUB format. Versions prior to 5.5 create EPUBs that require significant editing to pass ePubCheck or ePubPreFlight. As from InDesign CC 2014, InDesign can export in ePub3 fixed-layout format.
Adobe RoboHelp Windows Unknown Online documentation tool that supports export to EPUB format
Atlantis Word Processor Windows, Portable app Shareware Converts any document to EPUB; supports multilevel TOCs, font embedding, and batch conversion.
Booktype Web GPL Book production platform that outputs to many formats, including ePub. The platform can import content in various formats and supports collaborative editing.
calibre Windows, OS X, FreeBSD, Linux GPL Conversion software and e-book organizer. Allows plugins, including for editing EPUB files; there is for instance a plugin to merge several EPUB files into one.[42]
eLML Windows, OS X, FreeBSD, Linux Unknown The eLesson Markup Language is a platform-independent XML-based open source framework to create eLearning content. It supports various output formats like SCORM, HTML, PDF and also eBooks based on the ePub format.
Feedbooks Web Unknown Free cloud service for downloading public domain works and for self-publishing.
Help & Manual Windows Proprietary Single source publishing tool that generates ePUB amongst several other documentation formats.
HelpNDoc Windows Free for personal use, commercial otherwise. Help authoring tool that generates EPUB files and other formats.
iBooks Author OS X Unknown Desktop publishing and page layout application. Free from Apple. Can export .ibooks format, which is a proprietary format based on EPUB.[43] There are restrictions on the commercial distribution of works created with iBooks in the .ibooks format.[44] These restrictions apply to the .ibooks format only[45] and it can be argued that a file renamed to .epub is not distributed in the .ibooks format.
IGP:Digital Publisher Web Proprietary Portal Cloud Service or licence application for digital content publishing to all formats. Generates ePub 2 and ePub 3 fixed and flow layout plus other formats.
iStudio Publisher OS X Proprietary Desktop publishing and page layout application.
LibreOffice Windows, OS X, Linux Mozilla Public License, GNU Lesser General Public License Text processor with a functionality to export as ePub3 format since version 6.0. Also allowed to export as ePub format via installing extension, such as eLaix.[46]
Lulu.com Web Unknown Converts .doc, .docx, or PDF manuscripts to an ePub in order that they may be sold on the Website in question.
Madcap Flare Windows Proprietary Single source publishing tool that can export content as ePUB.
oXygen XML Editor OS X, Windows, FreeBSD, Linux Proprietary oXygen XML Editor is the first tool that supports creating, transforming, and validating the documents that comprise the EPUB package.
Pages OS X Unknown Word processor (part of the iWork '09 suite) that can export to EPUB format (Pages '09 only, and only with the iWork 9.0.4 update).
Pages Apple iOS Unknown Word processor for mobile devices that can export to EPUB format
Playwrite OS X Proprietary Native EPUB-based word processor. Native to EPUB 3 with EPUB 2 compatibility.
QuarkXPress OS X, Windows Proprietary Desktop publishing tool, page layout application. Exports also to the ePUB format.
Serif PagePlus Windows Proprietary Desktop publishing program that can export to the EPUB 2 and EPUB 3 format. Comes with built-in output conversion profiles for targeting specific devices, as well as generic devices. Also includes pre-tested blank eBook templates, or can open and edit existing PDF files and publish as EPUB.
Scrivener Windows, OS X Proprietary Program for writers. Includes organization capabilities for fiction writers. Publishes to multiple formats.
Sigil Windows, FreeBSD, Linux, OS X GPL Can open and edit EPUB books, instead of just converting from other formats to EPUB. Since version 0.7, supports embedding video or audio in EPUB. Development was stopped in February 2014, and launched again in September 2014 with version 0.8.0 released[47]
eXeLearning Windows, Linux, OS X GPL Can be used to create educational interactive Web content, HTML5, IMS, SCORM and EPUB3 books[48]


  1. ^ For a table of the required XHTML modules and a description of the restrictions, see "Section 2.2", ePub OPS 2.0.1 (specification draft), IDPF.
  2. ^ For a table of supported properties and detailed information, see "Section 3.0", ePub OPS 2.0.1 (specification draft), IDPF.
  3. ^ For a full listing of metadata, see "Section 2.2", ePub OPF 2.0.1 (specification draft), IDPF.
  4. ^ A list of possible values for type is in "Section 2.6", ePub OPDF 2.0.1 (specification draft), IDPF.
  5. ^ Detailed descriptions of the differences between 3.0 and 2.0.1 can be found on ePub 3.0 spec changes, IDPF.


  1. ^ "Specifications". IDPF. Retrieved January 12, 2017.
  2. ^ "OPS 2.0 Elevated to Official IDPF Standard". IDPF. eBooklyn. Oct 15, 2007.
  3. ^ "Endorsement of EPUB 3". BISG. Book Industry Study Group. Retrieved 18 September 2015.
  4. ^ "Older Versions of EPUB | International Digital Publishing Forum". idpf.org. Retrieved 2017-05-10.
  5. ^ a b "1.1 EPUB Revision History". IDPF. 11 October 2011.
  6. ^ "EPUB 3.0 | International Digital Publishing Forum". idpf.org. Retrieved 2017-01-12.
  7. ^ a b Rothman, David (July 27, 2008). "The ePub torture test: Starring 'Three Shadows,' a graphic novel". TeleRead: Bring the E-Books Home.
  8. ^ "EPUB 3.1 | International Digital Publishing Forum". idpf.org. Retrieved 2017-01-12.
  9. ^ "EPUB 3.1 Changes from EPUB 3.0.1". www.idpf.org. Retrieved 2017-01-12.
  10. ^ "EPUB 3.1 Changes from EPUB 3.0.1". www.idpf.org. Retrieved 2017-01-12.
  11. ^ "EPUB 3.1 Changes from EPUB 3.0.1". www.idpf.org. Retrieved 2017-01-12.
  12. ^ "IDPF Members Approve W3C Merger - Publishing Perspectives". 9 November 2016.
  13. ^ "World Wide Web Consortium (W3C) and International Digital Publishing Forum (IDPF) Explore Plans to Combine".
  14. ^ a b c d e f "Open Publication Structure (OPS) 2.0.1 – Recommended Specification". IDPF. September 4, 2010. Retrieved February 21, 2011.
  15. ^ a b c d e f g h "Open Packaging Format (OPF) 2.0.1 – Recommended Specification". IDPF. September 4, 2010. Retrieved February 21, 2011.
  16. ^ a b c d e "Open Container Format (OCF) 2.0.1 – Recommended Specification". IDPF. September 4, 2010. Retrieved February 21, 2011.
  17. ^ a b "Specifications for the Digital Talking Book". NISO. April 21, 2005.
  18. ^ a b "EPUB 101" (PDF). eBook Technologies. Retrieved 10 July 2014.
  19. ^ "EPUB 3 Overview Draft". EPUB 3 Working Group. IDPF. 11 October 2011. Retrieved 11 October 2011.
  20. ^ "Links, pointers, bookmarks, highlights: How should .epub do it?". FrontMatters. BookGlutton. March 29, 2008.
  21. ^ Rothman, David (November 5, 2007). "'Social annotation and the marketplace of ideas': Time for an IDPF annotation standard for books and other e-pubs!". TeleRead: Bring the E-Books Home.
  22. ^ EPUB 3.0.1 Changes, IDPF, retrieved July 8, 2014.
  23. ^ EPUB 3.0 Published as ISO Technical Specification, IDPF, retrieved August 28, 2018.
  24. ^ "Fixed-Layout Properties". International Digital Publishing Forum. Retrieved 11 September 2015.
  25. ^ a b "Understanding EPUB 3". EPUBZone. International Digital Publishing Forum. Retrieved 11 September 2015.
  26. ^ "Embedded MathML". IDPF. Retrieved 12 September 2015.
  27. ^ a b "Digital Book Standards FAQs". IDPF. November 20, 2006. Archived from the original on 2009-09-03.
  28. ^ Gelles, David (January 29, 2010). "Walls close in on e-book garden". The Financial Times.
  29. ^ Rothman, David (August 13, 2009). "Adobe-DRMed ePub isn't 'open': Why the New York Times urgently needs to clarify its Sony eBook Store article". TeleRead: Bring the E-Books Home. Archived from the original on October 14, 2009.
  30. ^ Biba, Paul (December 21, 2009). "Does the Nook use its own incompatible DRM scheme?". TeleRead: Bring the E-Books Home.
  31. ^ Biba, Paul (January 28, 2010). "iPad adds to the DRM mess? Apple ebook DRM exclusive to Apple hardware". TeleRead: Bring the E-Books Home.
  32. ^ Kendrick, James (January 28, 2010). "Who Really Needs an iPad?". JK On The Run.
  33. ^ Dickson, Dave (January 27, 2010). "EPUB, iPad and Content Interoperability". Digital Editions. Adobe.
  34. ^ Arnold Kim (January 19, 2012). "New ibooks not technically in epub format". MacRumors.
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  36. ^ "EPUB Publications". IDPF. Retrieved 12 September 2015.
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  39. ^ "Validation tool for EPUB. Contribute to w3c/epubcheck development by creating an account on GitHub". 9 February 2019 – via GitHub.
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  41. ^ 2.9.1 release notes, Abi source.
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  47. ^ Sigil dev.
  48. ^ eXeLearning.

External links

Adobe Digital Editions

Adobe Digital Editions (abbreviated ADE) is an ebook reader software program from Adobe Systems, built initially (1.x version) using Adobe Flash. It is used for acquiring, managing, and reading eBooks, digital newspapers, and other digital publications. The software supports PDF, XHTML (through the nonproprietary EPUB file type specification) and Flash-based content. It implements a proprietary scheme of Digital Rights Management ("DRM") which, since the version 1.5 release in May 2008, allows document sharing among multiple devices and user authentication via an Adobe ID. ADE is a successor to Adobe eBook Reader.Windows and OS X versions of Adobe Digital Editions were released on June 19, 2007. Previous versions of the software required version 9.0 of Adobe Flash Player. Starting with version 2.0, however, which relies on .NET Framework 3.5 on Windows, Flash Player is no longer supported. Adobe initiated development of a Linux version of ADE in 2007; however, this has not had any beta release or any formal updates.


Aldiko is an e-book reader application for the Android and iOS operating systems. It supports the EPUB format for digital publications and incorporates facilities for browsing online catalogs on thousands of books (including thousands of free public domain work) and downloading them directly into the user's personal library. The application features a bookshelf-like user interface that lets user navigate their collection of eBooks. It also provides a customizable reading experience through configurable font and background color, font size and type, margin size, display brightness, page turn mode, etc. Additionally, the application allows users to import their own books to read them on the go. Aldiko does not support font embedding.

Apple Books

Apple Books is an e-book reading and store application by Apple Inc. for its iOS and macOS operating systems and devices. It was announced, under the name iBooks, in conjunction with the iPad on January 27, 2010, and was released for the iPhone and iPod Touch in mid-2010, as part of the iOS 4 update. Initially, iBooks was not pre-loaded onto iOS devices, but users could install it free of charge from the iTunes App Store. With the release of iOS 8, it became an integrated app. On June 10, 2013, at the Apple Worldwide Developers Conference, Craig Federighi announced that iBooks would also be provided with OS X Mavericks in fall 2013. Prior to iOS 12 and macOS Mojave, the application was named iBooks.

It primarily receives EPUB content from the iBooks Store, but users can also add their own EPUB and PDF files via data synchronization with iTunes. Additionally, the files can be downloaded to iBooks through Safari or Apple Mail. It is also capable of displaying e-books that incorporate multimedia. According to product information as of March 2010, iBooks will be able to "read the contents of any page [to the user]" using VoiceOver.On January 19, 2012 at an education-focused special event in New York City, Apple announced the free release of iBooks 2, which can operate in landscape mode and allows for interactive reading. In addition, a new application, iBooks Author, was announced for the Mac App Store, allowing anyone to create interactive textbooks for reading in iBooks; and the iBooks Store was expanded with a textbook category. The iBooks Author Conference, the annual gathering of digital content creators around Apple's iBooks Author, has convened since 2015.iBooks was renamed to Apple Books alongside the release of iOS 12 and macOS Mojave in September 2018. It features a new variation of the San Francisco typeface known as "SF Serif."

Bluefire Reader

Bluefire Reader is an e-book reader application for Android, iOS and Windows operating systems that supports white-labelling. It supports the EPUB and PDF formats for digital publications and incorporates facilities for browsing online catalogs, and downloading them directly into the user's personal library. The application features a library that lets users navigate their collection of eBooks, as well as provides a customizable reading experience through configurable font and background color, font size and type, margin size, display brightness, page turn mode, etc. Additionally, the application allows users to import their own books to read them on the go.

Calibre (software)

Calibre (stylised calibre) is a cross-platform open-source suite of e-book software. Calibre supports organizing existing e-books into virtual libraries, displaying, editing, creating and converting e-books, as well as syncing e-books with a variety of e-readers. Editing books is supported for EPUB and AZW3 formats. Books in other formats like MOBI must first be converted to those formats, if they are to be edited.

Comparison of e-book formats

The following is a comparison of e-book formats used to create and publish e-books.

The EPUB format is the most widely supported vendor-independent XML-based (as opposed to PDF) e-book format; that is, it is supported by the largest number of e-Readers, including Amazon Kindle Fire (but not standard Kindle). See table below for details.


FBReader is an e-book reader for Linux, Microsoft Windows, Android, and other platforms.

It was originally written for the Sharp Zaurus and currently runs on many other mobile devices, like the Nokia Internet Tablets, as well as desktop computers. A preview of FBReaderJ (the Java port) for Google Android was released on April 13, 2008.

Supported formats include EPUB, FictionBook, HTML, plucker, PalmDoc, zTxt, TCR, CHM, RTF, OEB, mobi without DRM, and plain-text.

Google Play Books

Google Play Books (formerly Google eBooks) is an ebook digital distribution service operated by Google. Users can purchase and download ebooks and audiobooks from Google Play, which offers over five million titles, with Google claiming it to be the "largest ebooks collection in the world". Books can be read on a dedicated Books section on the Google Play website, through the use of a mobile app available for Android and iOS, through the use of select e-readers that offer support for Adobe Digital Editions, through a web browser and reading via Google Home. Users may also upload up to 1,000 ebooks in the PDF or EPUB file formats. Google Play Books is available in 75 countries.

Google Play Books was launched in December 2010, with a reseller program letting independent booksellers sell Google ebooks on their websites for a cut of sales. It also launched an affiliate program in June 2011, allowing website owners to earn a commission by referring sales to the then-named Google eBookstore. However, the reseller program ended in April 2012, with Google stating that it had "not gained the traction that we hoped it would" and "not met the needs of many readers or booksellers". The affiliate program closed for new signups in February 2012, with Google announcing that it would scale down the initiative, making it private and invitation-only.

The mobile Android app has seen several significant updates since its introduction, including different reading modes with color contrasts, support for text highlighting and note-taking, a zoomed-out view with easy page sliding in an effort to improve reading experiences for books not read cover-to-cover, a vertical scrolling mode for comic books, a "Night Light" feature that gradually filters blue light to reduce eye strain after sunset, using machine learning imaging technologies to expand speech bubbles in comics, and listening to audiobooks.

Play Books store has been noted to hold a lot of pirated content, which led Google to discontinue new sign-ups to its publisher program in 2015. The program was reopened only in 2018 when it incorporated an automated process to decline books found to contain extensive text copied from other books already in the store.

IBooks Author

iBooks Author (iBA) is an e-book authoring application by Apple Inc. Books created with iBooks Author export as .ibooks files and can be published to the Apple iBooks Store, or they may be exported as PDF.

Apple released iBooks Author on January 19, 2012 at an education-focused special event in New York City. Simultaneously, Apple also released iBooks 2 and a new iBooks Bookstore category for textbooks. The software is proprietary and available only for macOS. Apple offers it for free download in the Mac App Store.

Apple describes iBooks Author as a tool for "educators and smaller publishers to create their own books". Documents created by iBooks Author may only be sold for a fee if they are accepted by and distributed by Apple, but authors also have the option to distribute their work anywhere if the work is being distributed for free.Many aspects of a document may be edited in WYSIWYG fashion, including text, fonts, colors, foreground and background images, interactive widgets, and charts. Tables of contents and glossaries may be managed with some automation. The user interface and editing features have been described as nearly identical to Apple's Keynote and Pages products.Apple clarified its position on rights of ebooks generated by iBooks Author on Feb 3, 2012 to address some controversy that its ebooks could be sold only through the Apple Bookstore, specifying that only books carrying the .ibooks suffix were subject to such restrictions. Apple also specified that the use of the software to create text or PDF files are within the terms of its user agreement. To offer your book on the iBookstore, an International Standard Book Number, or ISBN, is recommended but not required. An ISBN is a standardized identifier for books and is necessary for industry-wide sales charts and data sharing. Note that you can only provide an ISBN during the initial book delivery.The output of iBooks Author is a proprietary Apple file format similar to the EPUB standard, but with extensions that prevent it from being universally readable or editable as an EPUB document. The format uses undocumented, proprietary XML namespaces and undocumented extensions to CSS.A new version of iBooks Author was released on October 23, 2012. It includes embedded fonts, mathematical equation rendering, and more interactivity options. On October 22, 2013, iBooks Author received another update which included compatibility with OS X Mavericks.

On October 16, 2014, Apple updated iBooks Author to version 2.2, adding several new features, namely EPUB import, InDesign IDML import, and the addition of a blank template for ease of use.On June 30, 2015, Apple updated iBooks Author to version 2.3, adding two significant new features: iPhone compatibility for Multi-Touch Format books created in iBooks Author, and export of EPUB-format books created in iBooks Author. Further, the terms and conditions of iBooks Author were changed to allow iBooks Author users to monetize EPUB-format books exported out of iBooks Author any way they choose.On October 7, 2015, Apple updated iBooks Author to version 2.4, adding minor updates including the new ability of EPUB-format books created in iBooks Author to use the Pop-Over widget, as well as minor enhancements to the interface and to EPUB-format book function. Version 2.5 was released in late 2016.

iBooks Author adoption has grown since version 2.2's release leading to the creation of the iBooks Author Conference which has taken place in Nashville, Tennessee, in October 2015 and October 2016. A follow-up conference for 2017 has been announced, keynoted by NASA astrophysicist Dr. Scott Bolton.

International Digital Publishing Forum

The International Digital Publishing Forum (IDPF) was a trade and standards association for the digital publishing industry, set up to establish a standard for electronic book publishing. It was responsible for the EPUB standard currently used by most e-readers.

Starting from the Open eBook (OEB) Publication Structure (1999), created loosely around HTML, it then defined the OPS (Open Publication Structure), the OPF (Open Packaging Format) and the OCF (Open Container Format). These formats are the basis for EPUB.

While the basic standards are now established (pages, hyperlinks, definition of table of contents, authors, etc.), some other standards intersect the hardware field, such as those for power and for features of the hardware reader devices, and are still undergoing change and evolution. Other standards for ecommerce (including Digital Rights Management), are tied to the way the ebook is sold or delivered, and are therefore controlled by vendors.

On January 30, 2017, IDPF was combined into the World Wide Web Consortium.


Kitabu is an EPUB reading application for macOS, released in 2012.


Lektz is an eBook business platform developed by AEL Data, operating from UK and India. The solutions available in the Lektz platform include DRM, ebook reader applications, virtual book store, ebook conversion, elending, consumer analytics, and digital marketing solutions for small, medium-sized publishers and independent authors. Dr. M.S. Mohammed Sadiq, Sr. Vice President of AEL Data, is the chief architect of the Lektz platform and it draws support from AEL Data's ePublishing, digitization, accessibility solutions and application development services.

The Lektz platform was launched as a SaaS based solution and as an on-premises solution using the publisher's infrastructure. This solution was presented as an ebook ecosystem at the London Book Fair 2013, by Dr.Sadiq and Lindsay MacLeod, Executive Director at AEL Data.

Lektz eBook Reader is a reader application for Android, iOS devices, and PC reader (web-based/Google Chrome Extension).It supports PDF, EPUB2 and EPUB3 ebook formats. It was launched by AEL Data Services in May, 2012. The Lektz reader provides full support to Non-DRM ebooks while the DRM support is limited to ebooks that are secured using the Lektz Proprietary DRM. The Lektz eBook Reader supports both Fixed Layout and Freeflow EPUB across varied platforms.


Lucifox is a discontinued free and open source add-on for the browser Mozilla Firefox that organizes, saves and manages ebooks, supporting EPUB 3 and EPUB 2 formatted books without DRM and retrieval of books from on-line book catalogues using the Open Publication Distribution System (OPDS). It is part of the Lucidor suite of free and open source ebook software made by the Swedish developer Ordbrand.


Okular is the multiplatform document viewer developed by the KDE community and based on Qt and KDE Frameworks libraries. It is distributed as part of the KDE Applications bundle. It was originally based on KPDF and it replaced KPDF, KGhostView, KFax, KFaxview and KDVI in KDE 4. Its functionality can be easily embedded in other applications.

Phosphatidylinositol 3,5-bisphosphate

Phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P2) is one of the seven phosphoinositides found in eukaryotic cell membranes.

In quiescent cells, the PtdIns(3,5)P2 levels, typically quantified by HPLC, are the lowest amongst the constitutively present phosphoinositides. They are approximately 3 to 5-fold lower as compared to PtdIns3P and PtdIns5P (Phosphatidylinositol 5-phosphate) levels, and more than 100-fold lower than the abundant PtdIns4P (Phosphatidylinositol 4-phosphate) and PtdIns(4,5)P2.

PtdIns(3,5)P2 was first reported to occur in mouse fibroblasts and budding yeast S. cerevisiae in 1997.

In S. cerevisiae PtdIns(3,5)P2 levels increase dramatically during hyperosmotic shock.

The response to hyperosmotic challenge is not conserved in most tested mammalian cells except for differentiated 3T3L1 adipocytes.

Sigil (application)

Sigil is free, open-source editing software for e-books in the EPUB format.

As a cross-platform application, Sigil is distributed for the Windows, macOS and Linux platforms under the GNU GPL license. Sigil supports both WYSIWYG and code-based editing of EPUB files, as well as the import of HTML and plain text files.Sigil has been developed by Strahinja Val Marković and others since 2009. From July 2011 to June 2015 John Schember was the lead developer. In June 2015 development of Sigil was taken over by Kevin Hendricks and Doug Massay.

Sony Reader

The Sony Reader was a line of e-book readers manufactured by Sony, who produced the first commercial E Ink e-reader with the Sony Librie in 2004. It used an electronic paper display developed by E Ink Corporation, was viewable in direct sunlight, required no power to maintain a static image, and was usable in portrait or landscape orientation.

Sony sold e-books for the Reader from the Sony eBook Library in the US, UK, Japan, Germany, Austria, Canada and was reported to be coming to France, Italy and Spain starting in early 2012. The Reader also could display Adobe PDFs, ePub format, RSS newsfeeds, JPEGs, and Sony's proprietary BBeB ("BroadBand eBook") format. Some Readers could play MP3 and unencrypted AAC audio files.

Compatibility with Adobe digital rights management (DRM) protected PDF and ePub files allowed Sony Reader owners to borrow ebooks from lending libraries in many countries.The DRM rules of the Reader allowed any purchased e-book to be read on up to six devices, at least one of which must be a personal computer running Windows or Mac OS X. Although the owner could not share purchased eBooks on others' devices and accounts, the ability to register five Readers to a single account and share books accordingly was a possible workaround.

On August 1, 2014, Sony announced that it would not make another consumer e-reader.

In late 2014, Sony released the Sony Digital Paper DPTS1 that is only aimed at professional business users that only view PDFs and it has a stylus for making notes.

Sumatra PDF

Sumatra PDF is a free and open-source document viewer that supports many document formats including: Portable Document Format (PDF), Microsoft Compiled HTML Help (CHM), DjVu, EPUB, FictionBook (FB2), MOBI, PRC, Open XML Paper Specification (OpenXPS, OXPS, XPS), and Comic Book Archive file (CB7, CBR, CBT, CBZ). If Ghostscript is installed, it supports PostScript files. It is developed exclusively for Microsoft Windows, but it can run under Linux using Wine.


Writer2ePub (W2E) is a free extension for the various implementations of the Writer text processor to create EPUB-formatted e-Books "from any file format that Writer can read". A text to be exported as EPUB has to be saved as OpenDocument (ODT)-formatted text document. Writer2epub is written in OpenOffice Basic. The author of Writer2ePub is Luca “Luke” Calcinai.


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