One of the most popular ebook formats—in terms of unit sales—is Amazon’s proprietary AZW format (also known as MOBI 7). AZW, which many speculate to stand for Amazon Whispernet (the cellular-based wireless service that Amazon uses to deliver books directly to your Kindle), is based on the original MOBI format developed by the French firm Mobipocket SA.

Amazon purchased Mobipocket in 2005, and incorporated the file format and digital rights management (DRM) system (with some tweaks) into the emerging Kindle standard. AZW is a proprietary format, which means that Amazon alone controls its future, along with which devices (or software applications) you can use to read books in the format.

In practical terms, this means that books in the AZW format are only readable using Amazon’s Kindle ereader, along with Amazon’s corresponding applications for the iPhone, iPad, Mac, PC, Blackberry, and other platforms.

Some argue that because Amazon readily supports most major platforms, consumers who invest in AZW-format books are making a safe decision since these books are, at present and for all intents and purposes, portable across the most common devices people are likely to own.

However, the proprietary nature of AZW means that Amazon can modify or even discontinue the format without regard to the needs of external parties. In fact, with Amazon’s introduction of Kindle Format 8 (the new format on which the Kindle Fire tablet is based), the future of AZW is now somewhat less than clear.

From an author or publisher’s perspective, proprietary formats can be tricky. While proprietary systems can lead to rapid and targeted innovation (without the need for messy group consensus that is so often the case with open standards), it does leave a considerable amount of power concentrated in the hands of one or very few parties.

Understanding AZW Features

In terms of features, AZW supports basic formatting including bold and italic text, simple tables (viewable on all but first-generation Kindles), and shaded areas to simulate sidebars (though everything appears in a single column).

AZW also allows you to include a table of contents (with hyperlinks), as well as internal cross-references within your books. When it comes to images, AZW allows you to include color photos and illustrations (the first image in your book is usually a full page cover).

The AZW format also lets you add Digital Rights Management to your ebook, preventing others from copying your work without permission. Your readers will need either a Kindle or Kindle application to read books protected using Amazon’s DRM system.

Strengths

AZW is a very simple format with few distractions. Consequently, AZW is one of the easier formats for authors and publishers.

Weaknesses

AZW suffers from many of the same limitations as other first-generation ebook formats, including limited support of typography and layout. Aside from that, there are no serious additional limitations.

Our Recommendation

Almost every ePublishing plan should include support for the AZW format (which is the current Amazon standard at the time of writing in November, 2011). However, it should not be the only format you support, even if the Kindle is your absolutely favorite ereader.

Some have argued that AZW is less suitable for books that absolutely demand color and high-resolution photographs or illustrations, though this has become less of an issue since Amazon announced the color-based Kindle Fire, and has long had an excellent color ereader application available for the iPad.

In general, Amazon AZW is best for the following types of ebooks:

• Most fiction (novel and short story anthologies, article collections)

• Memoirs (with basic layout requirements for photos and illustrations)

• General non-fiction

Amazon AZW is less well suited for the following types of ebooks:

• Textbooks

• Photo books (since some on your readers might be using black-and-white low-resolution Kindle devices)

• Other books that rely on color or layout to convey information