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 currently hosted by Ryan Seacrest and presented as an adjunct to his weekday radio program, On Air with Ryan Seacrest.
Originally a production of Watermark Inc. (later a division of ABC Radio known as ABC Watermark, now Cumulus Media Networks), AT40 is now distributed by Premiere Networks in the United States, Canada, Australia, the Philippines, Singapore, China, India, the United Kingdom, Malaysia and several other territories worldwide. It can also be heard on both the iHeartRadio application and the AT40 Mobile application on mobile smartphones and tablets as well as on Xbox 360 and Xbox One consoles.
Co-creator Casey Kasem hosted the original AT40 from its inauguration on July 4, 1970 until August 6, 1988. Shadoe Stevens took over the program on August 13, 1988 and hosted until January 28, 1995 when the original program came to an end. Three years later, Kasem teamed up with Premiere's predecessor AMFM Radio Networks to relaunch AT40. Kasem, who spent nine years hosting his own countdown for Westwood One, returned to hosting his creation on March 28, 1998. Seacrest took over AT40 on January 10, 2004 following Kasem's retirement from the series.
Currently, AT40 with Seacrest airs in two different formats, with one distributed to Contemporary Hit Radio (Top 40) stations and the other to Hot Adult Contemporary stations. However, there is no distinction made between the two shows on air. There are also two classic editions of the original AT40 distributed every weekend, featuring past Kasem-hosted shows from the 1970s and 1980s.
In its early years, the AT40 used the Billboard charts to compile the countdown, touting it as "the only source". The program subsequently switched to being based on Radio and Records airplay data upon its late 1990s return. The current source for the AT40 charts are the mainstream Top 40 and hot adult contemporary charts compiled by Mediabase, which are published in USA Today each Friday.