American Top 40

American Top 40 (commonly abbreviated to AT40) is an internationally syndicated, independent song countdown radio program created by Casey Kasem, Don Bustany, Tom Rounds and Ron Jacobs. The program is hosted by Ryan Seacrest, who took over the program from Kasem upon his 2004 departure. It is currently presented as an adjunct to Seacrest's weekday radio program, On Air with Ryan Seacrest.