The very first radio broadcast occurred in 1906, courtesy of Reginald Fessenden. Ships at sea heard him playing "O Holy Night" on his violin and then reading a verse from the Bible.
Radio experiments continued, and radio stations were established all over the country. The first actual commercial was broadcast in 1922 from radio station WEAF.
As radio became more popular, stations looked for ways to fill their airwaves with programming. In those early days, the commercials were read live on the air, and entire shows could be sponsored by a single advertiser.
Radio programming and advertising peaked during the 1930s and 1940s. Many of these shows were sponsored by advertisers pushing such products as cigarettes, tires and even coal.
After World War II, radio's popularity began to decline, and a new medium began to take shape. TVs began to gain in popularity, and advertisers were quick to notice.
Radio still earns its money through advertising today, although shows are generally no longer sponsored by single advertisers.