National Library Service for the Blind and Physically Handicapped (NLS)
The Library of Congress

The free Library service was established by an Act of Congress in 1931 to provide blind adults with books in an embossed format.  The Act was amended in 1934 to include sound recordings (talking books), and was expanded in 1952 to include children, in 1962 to provide music materials, and again in 1966 to include individuals with physical limitations that prevent the reading of regular print.

Talking books require the use of a specialized playback device.  Initially they were available on sets of special 10 inch 8 rpm records. Then they were made available on cassette, and specialized cassette players were available on loan to eligible readers.  In 2009, digital format books were introduced on easy-to-handle cartridges.  Two types of digital players are available: a standard model and an advanced model with navigation and bookmark features.  Current readers are encouraged to use both cassette and digital players to access the full range of the NLS collection.  NLS formats render the books unusable by the general public, a requirement under the U.S. copyright law to protect intellectual property while allowing NLS patrons free use of the material.

http://www.loc.gov/nls/index.html