Los 40 is a Spanish-language Top 40 music radio network and brand. It began in 1966 as a music show on Radio Madrid, and evolved into a stand-alone radio station in 1979. The show's first chart was the Los 40 Principales, which was broadcast on Cadena SER.
The program's format was simple: listeners would vote by phone or online to determine which songs were best, and the show would compile the top 40 on a weekly basis. The format was so popular that the show was later turned into a radio station. Although the station has changed its format, it has managed to stick to its original concept and is now one of the most popular stations in the country.