WMA Audiobooks are digitally-protected audiobook titles available for download in the Windows Media Audio (WMA) format. WMA Audiobooks are about half the file size of MP3 Audiobooks but maintain the same level of audio quality. WMA Audiobooks are generally compatible with portable devices that support DRM-protected WMA files encoded at a bit rate of 32kbps. For a list of supported devices, click here. MP3 Audiobooks are encoded at a bit rate of 64kbps and are available for download as MP3 files. MP3 Audiobooks are compatible with many devices including most cell phones, PDAs, and MP3 players. If you wish to transfer audiobooks to an Apple device (iPod, iPhone, etc.) or other device that plays MP3 audio files but does not support DRM-protected WMA files, you must check out MP3 Audiobooks. Note that OverDrive Media Console for Mac supports MP3 Audiobooks only, and transfers titles to Apple devices only.