When commercial radio stations began broadcasting in the early 1920s, the programs were aired without advertising.
Many radio stations were established by radio equipment manufacturers and retailers such as RCA and programming was provided to sell radio transmitters and receivers. Programming was financed from the sale of the equipment.
Other radio stations and programs were provided as a public service through endowments or municipal financing.
Some early radio stations were owned and operated by newspaper publishers. Radio gave an added forum to express the opinions of the owners and resulted in increased newspaper sales.
In effect, most early radio stations had only one sponsor, the company that owned the station. Before long, these companies began to provide their programs to independently owned radio stations, creating the first radio networks.
The radio station owners soon realized they could earn more money, by selling sponsorship rights to other businesses. In those days, each show was usually sponsored by a single business, in exchange for a brief mention of the sponsor at the beginning and end of the show.
In the early days of radio broadcasting, sustaining programming included a wide variety of shows offered by radio stations and networks to attract audiences to the new medium.
Radio stations needed to fill their broadcast schedule, whether of not they had a sponsor for each program. New programs would often go on the air unsponsored. If a radio station and it's shows became popular, then it was more likely to attract sponsors.
In the early 1950s, the DuMont Television Network began the modern trend of selling advertisement time to multiple sponsors. DuMont had trouble finding sponsors for many of their programs and compensated by selling smaller blocks of advertising time to several businesses.
Currently, most sustaining programming on commercial television is confined to public affairs, religious, and special news programs.
Non-commercial public radio stations are funded by donations and operate without advertising. However, many of their programs briefly acknowledge funding from commercial sponsors.