Kindle uses its own format called AZW, which Amazon created to lock books to their ecosystem

Amazon's Kindle devices and apps read AZW files — a format Amazon built specifically for Kindle. This is not the same as EPUB, the open standard that most other e-readers use. When you buy a book from Amazon, it arrives as an AZW file with digital rights management (DRM) built in, which means the file only opens on Kindle devices and apps, and only on the account that purchased it.

Amazon has released several versions of AZW over the years. The original AZW is based on an older format called Mobipocket. AZW3 (also called KF8) is the newer version that supports better formatting, including fonts and layouts closer to print books. Most Kindle devices sold today use AZW3, though older Kindles still read the original AZW format.

If you want to read a book on a non-Kindle device — an iPad, an Android tablet, a Kobo reader, or a computer — you cannot simply move the AZW file over. The DRM prevents that. You would need to either buy the book again from a store that supports your device, or convert the file using third-party software (which only works if you remove the DRM first, a legal gray area that varies by country).

Key Takeaways

  • Kindle books are stored in AZW or AZW3 format, which only Kindle devices and apps can read.
  • AZW3 is the current standard and supports better formatting than the older AZW format.
  • DRM protection on Kindle books ties them to your Amazon account and prevents moving files to other devices.
  • EPUB is the standard format used by most other e-readers, but Kindle does not support it natively.
  • You can read Kindle books on non-Kindle devices using Amazon's free Kindle reading apps for phones, tablets, and computers.

Why Amazon chose its own format instead of using EPUB

EPUB is the open standard for e-books, supported by nearly every e-reader except Kindle — Kobo, Apple Books, Google Play Books, and most library apps all use EPUB. Amazon could have adopted it, but chose not to because a proprietary format gives them control over the reading experience and ties customers to their ecosystem.

With AZW, Amazon controls which devices can read the books, how they display, and what features are available. This also makes it harder for readers to leave Kindle — if your library is in AZW format with DRM, moving to a Kobo or another reader means either leaving those books behind or going through a conversion process that may not be legal where you live.

From Amazon's perspective, this lock-in is a business advantage. From a reader's perspective, it means your book collection is less portable than it would be with EPUB.

What happens when you buy a Kindle book

When you purchase a book from the Kindle Store, Amazon sends you an AZW3 file encrypted with DRM tied to your Amazon account. The file downloads to your Kindle device or app automatically. You can read it on any device where you are signed into that Amazon account — your Kindle e-reader, your phone, your tablet, your computer — but the file itself stays encrypted and locked to you.

If you lend a Kindle book to someone (a feature Amazon offers for some titles), they receive a temporary copy that expires after 14 days. They cannot keep the file or read it after the loan period ends.

If you delete a book from your device, it is not gone — it stays in your Amazon library in the cloud. You can re-download it anytime. But if Amazon removes the book from the Kindle Store (which has happened), you lose the right to re-download it, though copies already on your devices remain readable.

How to move Kindle books to other devices

The straightforward legal route is to use Amazon's Kindle reading apps, which are free for iPhone, iPad, Android phones and tablets, Mac, Windows, and web browsers. If you own a Kindle book, you can read it on any of these devices by signing into your Amazon account. This is not moving the file — it is reading the same book through different apps — but it gives you access to your library across devices.

If you want to read a Kindle book on a non-Amazon e-reader like a Kobo or a Nook, you face a technical and legal barrier. The DRM on the file prevents direct transfer. Some readers use third-party software to strip the DRM and convert AZW to EPUB, but this is a legal gray area. In the United States, the Digital Millennium Copyright Act (DMCA) makes circumventing DRM illegal even for content you own, though enforcement against individual readers is rare. Other countries have different laws.

The practical reality: if you want your e-book library to be portable across devices, buying from stores that use EPUB (like Apple Books, Google Play, or Kobo) is simpler than buying from Kindle and then converting.

Sending documents to Kindle in other formats

Kindle devices have a feature called Send to Kindle that lets you email documents to your device. You can send PDF, DOCX, DOC, HTML, TXT, JPEG, GIF, BMP, and PNG files to a special email address Amazon assigns to your account. The device converts them and displays them as if they were Kindle books.

This is useful for reading your own documents — a research paper, a recipe collection, a family photo album — on your Kindle. The conversion is not always perfect; complex layouts in PDFs sometimes break. But for plain text and simple documents, it works well.

Documents you send to Kindle this way are not DRM-protected and stay in your personal library. You can also email documents to other people's Kindle devices if they have given you permission to use their Send to Kindle email address.

The difference between AZW and AZW3

The original AZW format was based on Mobipocket, an older e-book standard. It works on all Kindle devices, but it has limitations — it does not handle complex fonts, colors, or advanced layouts well. Books in AZW format often look plain and basic.

AZW3 (released in 2011 with the Kindle Fire) is Amazon's newer format. It supports better typography, embedded fonts, color, and more sophisticated page layouts. Most new Kindle books are published in AZW3. Older Kindle devices (like the basic Kindle Paperwhite from 2012 or earlier) may not read AZW3, but nearly all Kindles sold in the last decade do.

If you own an older Kindle device and try to download a new book, Amazon usually has an AZW version available as a fallback. But if you are buying a new Kindle today, you will be reading AZW3 files.

Can you convert AZW files yourself

Yes, but with caveats. Software like Calibre (free, open-source) can convert AZW to EPUB, PDF, or other formats. However, Calibre cannot remove DRM protection — if your Kindle book has DRM, Calibre will not touch it. You would need to use a separate tool to strip the DRM first, which is where the legal question arises.

If you have a DRM-free AZW file (some self-published books or books from non-Amazon sources come this way), Calibre can convert it without issue. But most books from the Kindle Store have DRM, so this route is not practical for most readers.

For documents you send to Kindle yourself, there is no DRM, so you can convert them freely using Calibre or any other tool.

Frequently Asked Questions

Can I read Kindle books on my iPad or Android tablet?

Yes. Download the free Kindle app from the App Store (iPad) or Google Play (Android), sign in with your Amazon account, and your Kindle library appears. You read the same books you own, just through the app instead of a Kindle device. The books are still AZW format, but the app handles the reading.

What happens if I buy a book in EPUB format by mistake?

Kindle devices and apps do not read EPUB files. If you download an EPUB book, you cannot open it on Kindle. You would need to convert it to AZW3 using software like Calibre, or read it on a different device or app that supports EPUB, like Apple Books or a Kobo reader.

If I delete a Kindle book from my device, can I get it back?

Yes. The book stays in your Amazon library in the cloud. Go to your Kindle library on Amazon.com or in the Kindle app, find the book, and select "Download" or "Send to Device." It re-downloads to your device. The only exception is if Amazon removes the book from the Kindle Store entirely, which is rare but has happened.

Do self-published books on Kindle use AZW3?

Usually yes. Authors who publish through Kindle Direct Publishing can upload in several formats (DOCX, PDF, EPUB), and Amazon converts them to AZW3 automatically. The final book on Kindle is in AZW3 format, just like traditionally published books.

Why does my old Kindle not show new books I bought?

Very old Kindle devices may not support AZW3. If your device is more than 10 years old, Amazon may only have an older AZW version available. Check your device's manual or Amazon's support page to see which format it reads. If it only reads AZW, newer books may not be available to you on that device, though you can still read them on the Kindle app on your phone or computer.