E-book Formats Explained — EPUB, MOBI, AZW3, PDF, and More

July 13, 2026

When I bought my first Kindle back in 2011, I assumed all e-books were the same. You download a file, you read it on your device, done. Then I tried to open a library book on it and hit the wall that every new e-reader owner eventually hits: format incompatibility.

E-books come in a bunch of different formats, and they're not all created equal. Some are open standards. Some are proprietary locks designed to keep you inside a specific ecosystem. Some are great for novels but terrible for comics. Some are basically just images stuffed into a folder and renamed.

Let's break them down so you know what you're actually dealing with.

What is the most common e-book format? ▼EPUB. It's the industry standard for everything except Kindle. Open, flexible, and widely supported.What e-book format does Kindle use? ▼Modern Kindles use AZW3 and KFX. Older ones used MOBI. Kindle now accepts EPUB via Send to Kindle with automatic conversion.What is the difference between MOBI and AZW3? ▼AZW3 is the newer format with better typography and formatting. MOBI is the older, simpler format. Both are Amazon proprietary.What does CBZ and CBR mean? ▼They're image archives for comics. CBZ is ZIP-based, CBR is RAR-based. Both store full-resolution page scans for comic reading apps.Can I convert between e-book formats? ▼Yes, with the right tools. DRM-free books convert easily between formats. DRM-protected books are locked to their ecosystem.