Audiobooks in the private domain are distributed online by for-profit companies. Most major audiobook publishers insist that their works, when sold as downloads, be protected by Digital Rights Management (DRM). Apple Inc. has licensed its proprietary FairPlay DRM system (for DRM protection of iPod files in the .aa file format) to only one company.

 

Because of the major publishers' insistence on DRM, this has effectively created a monopoly in the sale of the works of major publishers to iPod users, who make up the majority of the portable audio market.