Warren wrote over 800 songs between 1918 and 1981, publishing over 500 of them. They were written mainly for 56 feature films or were used in other films that used Warren's newly written or existing songs. His songs eventually appeared in over 300 films and 112 of Warner Bros. "Looney Tunes" and "Merrie Melodies" cartoons. 42 of his songs were on the top ten list of the radio program "Your Hit Parade", a measure of a song's popularity. 21 of these reached number 1 on Your Hit Parade. "You'll Never Know" appeared 24 times. His song "I Only Have Eyes for You" is listed in the list of the 25 most-performed songs of the 20th Century, as compiled by the American Society of Composers, Authors, and Publishers (ASCAP). Warren was the director of ASCAP from 1929 to 1932.