American Top 40 is a weekly radio countdown show that features the most popular songs in the United States. Created by Casey Kasem in 1970, it showcases the top 40 hits based on sales, radio airplay, and streaming data. The show has become a staple in American pop culture, influencing music trends and introducing listeners to new artists. Over the years, American Top 40 has had various hosts, including Ryan Seacrest, who took over in 2004. The program not only highlights current hits but also includes interviews and trivia about the artists and songs, making it an engaging experience for music fans.