The extension .AZW3 refers to files of the type, Amazon KF8 eBook files. This file type refers to ebooks created in the Amazon Kindle ebook format. It is also known as the KF8 format.

The file structure of AZW3 file is an enhanced version of the standard azw file format used by Amazon earlier. The newer version has support for HTML5, CSS3 and several other formatting techniques. The newer ebook format also has added features for rights protection and anti-piracy with its DRM protection. A free command line tool, KindleGen is provided by Amazon for users interested in creating their own kindle ebook files.